Add UI for CI_JOB_TOKEN permission settings

What does this MR do and why?

Implements #465375 (closed). Depends on !154111 (merged).

This adds the UI and documentation for allowing jobs write access to the project when they use the CI_JOB_TOKEN. Since the feature uses the allow_push_repository_for_job_token feature flag, the UI setting is also hidden behind the same feature flag.

Documentation leads to https://docs.gitlab.com/ee/ci/jobs/ci_job_token.html#push-to-a-project-repository-using-a-job-token.

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Screenshots or screen recordings

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	Screen_Recording_2024-06-28_at_16.11.23

How to set up and validate locally

1. Enable the feature flag

   rails c
   Feature.enable(:allow_push_repository_for_job_token, <project>)

2. Go to /-/settings/ci_cd and expand the Token Access section.
3. Allow push to the repository should be disabled by default.
4. Check the checkbox and save the changes. A toast message should pop up when the update is successful.
5. Changes persist when you refresh the page.