What does this PR do?

Provides the options for users to store and use their API keys as jenkins credentials in the jenkins UI.

Description of the Change

• Adds another input field in the gui for users to enter the API key as a credential
• Does not provide a way to pass it as an environment variable or call the function directly.
• Credential API key is always favored over the text input API key if one has been supplied
• Creates a new field and variable in the global configuration to maintain compatibility with those updating and continue to the text input API key
  Code changes are based on recommendations and guidance in https://github.com/jenkinsci/credentials-plugin/blob/master/docs/consumer.adoc

Alternate Designs

Possible Drawbacks

Verification Process

Additional Notes

Release Notes

Review checklist (to be filled by reviewers)

• Feature or bug fix MUST have appropriate tests (unit, integration, etc...)
• PR title must be written as a CHANGELOG entry (see why)
• Files changes must correspond to the primary purpose of the PR as described in the title (small unrelated changes should have their own PR)
• PR must have one changelog/ label attached. If applicable it should have the backward-incompatible label attached.
• PR should not have do-not-merge/ label attached.
• If Applicable, issue must have kind/ and severity/ labels attached at least.