Resolve "Container Registry: Allow toggling redirects to storage backends on a per-repository basis"

What does this MR do?

Enables the user to pass redirect exceptions via Helm values.

Related issues

#2381 (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

• Merge Request Title and Description are up to date, accurate, and descriptive
• MR targeting the appropriate branch
• MR has a green pipeline on GitLab.com

Expected (please provide an explanation if not completing)

• Test plan indicating conditions for success has been posted and passes
• Documentation created/updated
• Tests added
• Integration tests added to GitLab QA
• Equivalent MR/issue for omnibus-gitlab opened

Testing

Here's a values file to use to confirm this is working:

$ cat testing.values.yaml
registry:
  image:
    repository: registry.gitlab.com/gitlab-org/container-registry
    tag: v2.12.0-gitlab-pre
  storage:
    redirect:
      disable: false
      exceptions:
        - group-a/project-a.*
        - group-b/.*

certmanager-issuer:
  email: no@no.com

$ helm template -f test.values.yaml gitlab . | grep exceptions: -B2 -A2
      redirect:
        disable: false
        exceptions:
          - group-a/project-a.*
          - group-b/.*

You can see the exceptions are listed in the configuration.

{"go_version":"go1.14.5","instance_id":"38ccbf48-265e-4601-a6fd-676b8fb4f8cc","level":"info","msg":"redis not configured","service":"registry","time":"2020-11-19T22:24:30Z","version":"v2.9.1-gitlab-503-g253a66ac"}
{"go_version":"go1.14.5","instance_id":"38ccbf48-265e-4601-a6fd-676b8fb4f8cc","level":"info","msg":"Starting upload purge in 59m0s","service":"registry","time":"2020-11-19T22:24:30Z","version":"v2.9.1-gitlab-503-g253a66ac"}
{"exceptions":["group-a/project-a.*","group-b/.*"],"go_version":"go1.14.5","instance_id":"38ccbf48-265e-4601-a6fd-676b8fb4f8cc","level":"warning","msg":"redirect enabled with exceptions, this feature is temporary and will be removed in a future version","service":"registry","time":"2020-11-19T22:24:30Z","version":"v2.9.1-gitlab-503-g253a66ac"}
{"go_version":"go1.14.5","instance_id":"38ccbf48-265e-4601-a6fd-676b8fb4f8cc","level":"info","msg":"using inmemory blob descriptor cache","service":"registry","time":"2020-11-19T22:24:30Z","version":"v2.9.1-gitlab-503-g253a66ac"}
{"go_version":"go1.14.5","instance_id":"38ccbf48-265e-4601-a6fd-676b8fb4f8cc","level":"info","msg":"listening on [::]:5000","service":"registry","time":"2020-11-19T22:24:30Z","version":"v2.9.1-gitlab-503-g253a66ac"}

Closes #2381 (closed)