Add CI/CD access token section in project settings

What does this MR do?

This MR adds the "Token Access" section to the CI/CD settings for projects, allowing to enable or disable the access to the CI_JOB_TOKEN variable.

This feature is behind the ci_scoped_job_token feature flag.

How to test

• Enable ci_scoped_job_token locally in the rails console
• Visit a projects CI/CD settings and expand the token access section
• Test out functionality (add, remove, toggle etc.)

Related to: #328553 (closed)

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Error handling examples

Does this MR meet the acceptance criteria?

Conformity

• I have included a changelog entry, or it's not needed. (Does this MR need a changelog?)
• I have added/updated documentation, or it's not needed. (Is documentation required?)
• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.