Adds an GitHub Action to check all local (non http://, https:// ) links in all Markdown files of the repository for liveness.
Fails if a file is not found.

# Goal
This should help maintaining the quality of the documentation.

# Impact
Takes ~24 seconds currently and found 3 dead links (pull requests already created).

# Dependent PRs
* #2064 
* #2065 
* #2066

# Info
See [markdown-link-check](https://github.com/marketplace/actions/markdown-link-check).

# Example output
```
FILE: ./docs/profiling.md

1 links checked.

FILE: ./docs/plugins_guidelines.md

37 links checked.

FILE: ./docs/linters.md
[✖] ../.github/linters/markdown-lint.yml → Status: 400 [Error: ENOENT: no such file or directory, access '/github/workspace/.github/linters/markdown-lint.yml'] {
  errno: -2,
  code: 'ENOENT',
  syscall: 'access',
  path: '/github/workspace/.github/linters/markdown-lint.yml'
}
```

# Improvements
* Can also be used to check external links, but fails because of:
  * Too many requests (429) responses:
```
FILE: ./CHANGELOG.md
[✖] #1762 → Status: 429
```
   * crates.io links respond 404
```
FILE: ./README.md
[✖] https://crates.io/crates/bevy → Status: 404
```

Adds an GitHub Action to check all local (non http://, https:// ) links in all Markdown files of the repository for liveness.
Fails if a file is not found.

# Goal
This should help maintaining the quality of the documentation.

# Impact
Takes ~24 seconds currently and found 3 dead links (pull requests already created).

# Dependent PRs
* bevyengine#2064 
* bevyengine#2065 
* bevyengine#2066

# Info
See [markdown-link-check](https://github.com/marketplace/actions/markdown-link-check).

# Example output
```
FILE: ./docs/profiling.md

1 links checked.

FILE: ./docs/plugins_guidelines.md

37 links checked.

FILE: ./docs/linters.md
[✖] ../.github/linters/markdown-lint.yml → Status: 400 [Error: ENOENT: no such file or directory, access '/github/workspace/.github/linters/markdown-lint.yml'] {
  errno: -2,
  code: 'ENOENT',
  syscall: 'access',
  path: '/github/workspace/.github/linters/markdown-lint.yml'
}
```

# Improvements
* Can also be used to check external links, but fails because of:
  * Too many requests (429) responses:
```
FILE: ./CHANGELOG.md
[✖] bevyengine#1762 → Status: 429
```
   * crates.io links respond 404
```
FILE: ./README.md
[✖] https://crates.io/crates/bevy → Status: 404
```