feat(node): remove `users` from `Node`

By using groups, we can achieve the same which was only possible with `users` in `Node` before.
Users which were previously present in the `users` field in `Node` now need to be mapped to a group instead.

The mention of `Node Manager for` in the frontend was removed, due to the dynamic nature of Groups and Permissions in the new implementation and will be replaced in the future by a list of Groups instead.

Users which either have the `Node Viewer` or `Node Admin` permission will also see all of the projects in the list of projects which are associated to their node (similar to `Node Manager` previously).

Closes #352

Signed-off-by: martinfrancois <f.martin@fastmail.com>