Bugfix: Add each new user to the global extension project

[JNKielmann]

Extensions that should be available for all users are installed into the global extension project. All users need read access to this project so they can access the extension services running there.

The code for adding a new user to the global extension project was added at the end of the create_user_project function because it is already called for each new user. It was renamed to setup_user because it now not only creates the user project.

Maybe instead this setup_user function could also be removed entirely and the user permission setup is instead done directly in the create_user function. That would also prevent the accidental creation of a user without calling the setup_user function. I could update this PR if that would be the preferred solution.

[lukasmasuch]

The change makes sense 👍 Moving it directly to create_user seems to be fine for me, but I'm not completely sure if it had any reason that user creation and user setup are separated in the system initialization. That might need to be tested further.