Remove feature flag ci_job_token_scope

What does this MR do and why?

In this MR, we would like to remove the feature flag ci_job_token_scope and release the feature. And update the documentation to talk about the feature.

To test out this feature, you can try to disable/enable the flag through this guide: https://docs.gitlab.com/ee/api/container_registry.html. With the flag disabled, it should return a 403 and should work with the flag enabled. With the removal of the feature flag, the endpoints in that guide would be accessible.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #300821 (closed)

Related to https://gitlab.com/gitlab-com/ops-sub-department/section-ops-request-for-help/-/issues/238