API: Add environment action with /stop action

What does this MR do?

Add environments /stop endpoint

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

API v3 should remain working as before.

Why was this MR needed?

In Merge Request !6669 (merged) Delete dynamic environments the button to Destroy an environment was replaced by a button to Close/Stop the environment.

But the API endpoint was not deleted/changed. So change the API so it also possible to stop an environment through the API.

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?

Closes #27142 (closed)