notebook spawn requires maintainer permissions

[rokroskar]

Because we try to check the project's environment variables in the spawner code, the developer permissions are no longer enough to launch a notebook.

The line in question is

renku-notebooks/jupyterhub/spawners.py

Line 131 in 6fa857f

variable.key: variable.value for variable in gl_project.variables.list()

We should either fail gracefully here on a 403 or remove this - to my knowledge it is not being used.