feat(gui): allow changing workflow access level - #4161

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### What changes were proposed in this PR?
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Previously, when a user was given access to a workflow, the access level
(READ/WRITE) could not be changed directly. Users had to revoke access
and re-add with the new level. This PR adds the ability for users with
write access to change the access level of other users via a dropdown.

**Frontend (`share-access.component.ts` /
`share-access.component.html`):**
  - Added `hasWriteAccess` that checks write access.
- Added `changeAccessLevel()` method with confirmation warning when a
user downgrades their own access from WRITE to READ.
  - Dropdown disabled for users without write access.

  **Backend (`WorkflowAccessResource.scala`):**
- Modified `grantAccess` endpoint to allow users with WRITE access to
modify their own access level

  **Behavior:**
- Users with WRITE access can change other users' access levels via
dropdown
  - Users with WRITE access can downgrade their own access to READ
  - Owner's access cannot be changed

  **Demo:**



https://github.com/user-attachments/assets/cca50be0-b086-47c1-b4ae-2f10a60b51e9



### Any related issues, documentation, discussions?
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No

### How was this PR tested?
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Manually tested.

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Revised with Claude Code.

---------

Co-authored-by: Xiaozhen Liu <[email protected]>

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  2. Ensure you have added or run the appropriate tests for your PR
  3. If the PR is work in progress, mark it a draft on GitHub.
  4. Please write your PR title to summarize what this PR proposes, we 
    are following Conventional Commits style for PR titles as well.
  5. Be sure to keep the PR description updated to reflect all changes.
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### What changes were proposed in this PR?
<!--
Please clarify what changes you are proposing. The purpose of this
section
is to outline the changes. Here are some tips for you:
  1. If you propose a new API, clarify the use case for a new API.
  2. If you fix a bug, you can clarify why it is a bug.
  3. If it is a refactoring, clarify what has been changed.
  3. It would be helpful to include a before-and-after comparison using 
     screenshots or GIFs.
  4. Please consider writing useful notes for better and faster reviews.
-->

Previously, when a user was given access to a workflow, the access level
(READ/WRITE) could not be changed directly. Users had to revoke access
and re-add with the new level. This PR adds the ability for users with
write access to change the access level of other users via a dropdown.

**Frontend (`share-access.component.ts` /
`share-access.component.html`):**
  - Added `hasWriteAccess` that checks write access.
- Added `changeAccessLevel()` method with confirmation warning when a
user downgrades their own access from WRITE to READ.
  - Dropdown disabled for users without write access.

  **Backend (`WorkflowAccessResource.scala`):**
- Modified `grantAccess` endpoint to allow users with WRITE access to
modify their own access level

  **Behavior:**
- Users with WRITE access can change other users' access levels via
dropdown
  - Users with WRITE access can downgrade their own access to READ
  - Owner's access cannot be changed

  **Demo:**



https://github.com/user-attachments/assets/cca50be0-b086-47c1-b4ae-2f10a60b51e9



### Any related issues, documentation, discussions?
<!--
Please use this section to link other resources if not mentioned
already.
1. If this PR fixes an issue, please include `Fixes apache#1234`, `Resolves
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or `Closes apache#1234`. If it is only related, simply mention the issue
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  2. If there is design documentation, please add the link.
  3. If there is a discussion in the mailing list, please add the link.
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No

### How was this PR tested?
<!--
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Manually tested.

### Was this PR authored or co-authored using generative AI tooling?
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Revised with Claude Code.

---------

Co-authored-by: Xiaozhen Liu <[email protected]>

<!--
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1. If this is your first time, please read our contributor guidelines:
[Contributing to
Texera](https://github.com/apache/texera/blob/main/CONTRIBUTING.md)
  2. Ensure you have added or run the appropriate tests for your PR
  3. If the PR is work in progress, mark it a draft on GitHub.
  4. Please write your PR title to summarize what this PR proposes, we 
    are following Conventional Commits style for PR titles as well.
  5. Be sure to keep the PR description updated to reflect all changes.
-->

### What changes were proposed in this PR?
<!--
Please clarify what changes you are proposing. The purpose of this
section
is to outline the changes. Here are some tips for you:
  1. If you propose a new API, clarify the use case for a new API.
  2. If you fix a bug, you can clarify why it is a bug.
  3. If it is a refactoring, clarify what has been changed.
  3. It would be helpful to include a before-and-after comparison using 
     screenshots or GIFs.
  4. Please consider writing useful notes for better and faster reviews.
-->

Previously, when a user was given access to a workflow, the access level
(READ/WRITE) could not be changed directly. Users had to revoke access
and re-add with the new level. This PR adds the ability for users with
write access to change the access level of other users via a dropdown.

**Frontend (`share-access.component.ts` /
`share-access.component.html`):**
  - Added `hasWriteAccess` that checks write access.
- Added `changeAccessLevel()` method with confirmation warning when a
user downgrades their own access from WRITE to READ.
  - Dropdown disabled for users without write access.

  **Backend (`WorkflowAccessResource.scala`):**
- Modified `grantAccess` endpoint to allow users with WRITE access to
modify their own access level

  **Behavior:**
- Users with WRITE access can change other users' access levels via
dropdown
  - Users with WRITE access can downgrade their own access to READ
  - Owner's access cannot be changed

  **Demo:**



https://github.com/user-attachments/assets/cca50be0-b086-47c1-b4ae-2f10a60b51e9



### Any related issues, documentation, discussions?
<!--
Please use this section to link other resources if not mentioned
already.
1. If this PR fixes an issue, please include `Fixes apache#1234`, `Resolves
apache#1234`
or `Closes apache#1234`. If it is only related, simply mention the issue
number.
  2. If there is design documentation, please add the link.
  3. If there is a discussion in the mailing list, please add the link.
-->

No

### How was this PR tested?
<!--
If tests were added, say they were added here. Or simply mention that if
the PR
is tested with existing test cases. Make sure to include/update test
cases that
check the changes thoroughly including negative and positive cases if
possible.
If it was tested in a way different from regular unit tests, please
clarify how
you tested step by step, ideally copy and paste-able, so that other
reviewers can
test and check, and descendants can verify in the future. If tests were
not added,
please describe why they were not added and/or why it was difficult to
add.
-->

Manually tested.

### Was this PR authored or co-authored using generative AI tooling?
<!--
If generative AI tooling has been used in the process of authoring this
PR,
please include the phrase: 'Generated-by: ' followed by the name of the
tool
and its version. If no, write 'No'. 
Please refer to the [ASF Generative Tooling
Guidance](https://www.apache.org/legal/generative-tooling.html) for
details.
-->

Revised with Claude Code.

---------

Co-authored-by: Xiaozhen Liu <[email protected]>