Specify patchable type

## OpenProject Work Packages

* https://community.openproject.org/work_packages/17420
* https://community.openproject.org/work_packages/17421
* https://community.openproject.org/work_packages/17422

## Changes

* type linked in WP rather than named
* new endpoints
    * type by id
    * all types
    * type by project
* project links to available types
Now you know why I am asking! ^^

I know that it is standard to let the server decide what to embed, but don't we want to provide some sort of hint regarding this?