API: replace environments `destroy` endpoint with `stop` endpoint

Summary

In Merge Request !6669 (merged) 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 reflects the same functionality.

Possible fixes

• Remove the delete action from the environments API.
• Add stop action to the environments API.

Related issues

#26479 (closed) #24147 (closed) #20070 (closed)