Add config support for container registry garbage collection

What does this MR do?

This merge request adds support for the container registry garbage collection configuration (see https://gitlab.com/gitlab-org/container-registry/-/blob/master/docs/configuration.md?ref_type=heads#gc) to omnibus-gitlab. It allows to fine-tune the garbage collection or disable it completely

Inspired by Add config support for container registry database (!7100 - merged).

/cc @hswimelar

🛠 with ❤ at Siemens

Related issues

Closes Container Registry: expose garbage collection c... (#8438 - closed).

Checklist

See Definition of done.

For anything in this list which will not be completed, please provide a reason in the MR discussion.

Required

• MR title and description are up to date, accurate, and descriptive.
• MR targeting the appropriate branch.
• Latest Merge Result pipeline is green. -> Unrelated build failure due to the lack of access token, since it's contributed from the community repo.
• When ready for review, MR is labeled "~workflow::ready for review" per the Distribution MR workflow.

For GitLab team members

If you don't have access to this, the reviewer should trigger these jobs for you during the review process.

• The manual Trigger:ee-package jobs have a green pipeline running against latest commit.
• If config/software or config/patches directories are changed, make sure the build-package-on-all-os job within the Trigger:ee-package downstream pipeline succeeded.
• If you are changing anything SSL related, then the Trigger:package:fips manual job within the Trigger:ee-package downstream pipeline must succeed.
• If CI configuration is changed, the branch must be pushed to dev.gitlab.org to confirm regular branch builds aren't broken.

Expected (please provide an explanation if not completing)

• Test plan indicating conditions for success has been posted and passes.
  • Tested with a local gitlab-ce omnibus installation:
    • When disabled: true
      • the config gets properly templated
      • the registry shows no gc metrics
      • the registry doesn't delete a non-current manifest
    • When disabled: false and reviewafter: 1h
      • the config gets properly templated
      • the registry shows gc metrics with successful runs
      • the registry deletes a non-current manifest
• Documentation created/updated.
  • Registry GC documentation exists at https://gitlab.com/gitlab-org/container-registry/-/blob/master/docs/configuration.md?ref_type=heads#gc
• Tests added.
• Integration tests added to GitLab QA.
  • Registry GC use cases not covered by GitLab QA
• Equivalent MR/issue for the GitLab Chart opened.
  • Already exists, see Add online GC configurations to registry chart (gitlab-org/charts/gitlab!1908 - merged).
• Validate potential values for new configuration settings. Formats such as integer 10, duration 10s, URI scheme://user:passwd@host:port may require quotation or other special handling when rendered in a template and written to a configuration file.