WIP: Implement API endpoint to get all builds in an environment

What does this MR do?

It implements a new API endpoint, GET /projects/:id/environments/:environment_id/builds, which allows the retrieval of all builds belonging to a certain environment

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

All of it, essentially, since I have no previous experience w/ Grape and no clue if I did the right thing, especially when checking permissions.

Why was this MR needed?

The motivation for this MR is described in #25084 (moved)

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• 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?

#25084 (moved)