Allow using connector ID as oidc groups prefix

[corest]

Overview

Adds prefixes for OIDC groups. I'm not sure if we want to implement this on a different level (middleware?).
But I've been using this for some time and it works fine for my use-case, which is mostly about the security side, not UX.
E.g. it is not possible to configure the exact OIDC prefix with this, but as connector IDs are unique - it makes OIDC groups unique as well. I'm open for discussion if this approach is not how the community would like to solve this. For me, it works and closes the issue #918, therefore, sharing this solution here.

Usage: "Closes #918"

Special notes for your reviewer

Does this PR introduce a user-facing change?

This change allows enabling OIDC groups prefixes with connector IDs values. Having this makes it impossible for groups from different connectors to impersonate other group access by using the same group names.

This feature can be enabled with oidcGroupsPrefix: true. If this option is missing, it will be disabled by default. So it doesn't require any changes if you're updating from the old version

[sagikazarmark]

Thanks @corest!

We might put a hold on it in favor of #1635, but it's definitely a good use case.

[corest]

Ok then. Closing

[marians]

For the future visitor: the proposed implementation is lacking the prefixing when refreshing the token.