Resolve "Pages API"

What does this MR do?

Add's CRUD API end points for Pages Domains.

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

Yes! 😄

• Is it appropriate to expose raw certificate and key? See pages/domains/:domain/details.
• This introduces ability to edit an existing domain that is not possible in the UI. Primary use cases are:
  • Update expiring certificate
  • Convert existing domain from http to https
• Is API json schema correctly declared?
  • Should there be a distinction between a single domain response and a list response?
• Review security policy (probably a separate issue but here for reference)
  • The existing Domain Pages UI controllers only utilize authorize_read_pages and authorize_update_pages.
  • Current policy… (owner,admin: remove_pages), (master: admin_pages,read_pages,update_pages)
• Are the tests handled in a reasonable way?
  • Does every role need to be tested?
• Should the endpoints be disabled and return a particular response code if the pages facility is not enabled? See require_pages_enabled.

Why was this MR needed?

Through the API, it is not currently possible to add, update, or remove pages domains with optional certificate on projects. Requested in issue #23000 (moved).

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
  • All builds are passing
• 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
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closes #23000 (moved)