Disable pipelines on instance

What does this MR do?

Allows GitLab administrator to disable pipelines on the instance by preventing project admins from enabling pipelines on projects.

Are there points in the code the reviewer needs to double check?

I've never used Cycle Analytics, and I don't know how much sense it makes to keep it when pipelines are disabled, or if perhaps just some of it should be hidden. Please advise.

Why was this MR needed?

We provide an external CI/CD solution alongside our GitLab instance for our users and do not support the use of GitLab pipelines.

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Review
  • Has been reviewed by UX
  • Has been reviewed by Frontend
  • Has been reviewed by Backend
  • Has been reviewed by Database
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together

What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ce/issues/26347 https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/13504