[GitLab] allow union of allowed_users and {allowed_gitlab_groups, allowed_project_ids}

[floriandeboissieu]

Bug description

This issue is similar to #396 . In GitLab Oauth any reason for keeping the intersection between allowed_users and {allowed_gitlab_groups, allowed_project_ids} knowing that there is also a blocked_users configuration argument?

I labelled it as a bug because I don't see any reason for that and it seems counter-intuitive to be able to union members of groups and projects but not with allowed_users list. But I am new to jupyterhub so... and referring to #396 it seems to be a change from a previously available union behaviour, thus I am sorry if it is an intended behaviour.

Expected behaviour

It would be expected to have a union here, to invite users external to all groups or projects

Actual behaviour

At the moment, the users allowed to login are the intersection of allowed_users and the members of {allowed_gitlab_groups, allowed_project_ids}.

Workaround

Creating a group for non-members users, but that is not very sustainable :-)

[welcome]

Thank you for opening your first issue in this project! Engagement like this is essential for open source projects! 🤗

If you haven't done so already, check out Jupyter's Code of Conduct. Also, please try to follow the issue template as it helps other other community members to contribute more effectively.

You can meet the other Jovyans by joining our Discourse forum. There is also an intro thread there where you can stop by and say Hi! 👋

Welcome to the Jupyter community! 🎉

[consideRatio]

Fixed by #594