Mark Sidekiq queue selector as no longer experimental

What does this MR do?

In gitlab-org/gitlab!46562 (merged), we made the Sidekiq queue selector available without the 'experimental' prefix.

We now have two options: queueSelector and experimentalQueueSelector. If either is set, the Sidekiq pod in question will use the queue selector syntax. The experimentalQueueSelector option will be removed at some point in the future, but not before GitLab 14.0.

Related issues

gitlab-com/gl-infra/scalability#147 (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
• Equivalent MR/issue for omnibus-gitlab opened - gitlab-org/omnibus-gitlab!4714 (merged)