[APIv3] Specify status endpoint and edit form for WP

Specifies:
* [#17012](https://community.openproject.org/work_packages/17012)
* [#16971](https://community.openproject.org/work_packages/16971)

This PR introduces specification for:
* The full reading part of the statuses endpoint
* PATCH-ing the status of a work package
* edit forms to define which parts of a resource can be changed and which restrictions there are

To Do
-------

- [ ] verify permissions needed to view statuses (currently "view work package anywhere")
- [ ] Specify first set of action-links (will be required for forms)
- [ ] Specify form endpoint
spelling error "workpackage" -> "work package"