API: Moved `DELETE /projects/:id/star` to `POST /projects/:id/unstar`
What does this MR do?
Moves the unstar API endpoint from
POST to make it more restful.
Does this MR meet the acceptance criteria?
- Changelog entry added
- Documentation created/updated
- API support added
- 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