Display labels on spaces projects

Add a 'relation' field to spaces projects.

To test:

%> bundle exec rails db:reset

GET /api/spaces/1/projects you will see a relation field.

Pagy still works GET /api/spaces/1/projects?items=1&page=3 will return a single value, the same as the last value above.

Closes https://gitlab.com/JOGL/JOGL/-/issues/890