Add additional specs to document current behaviour on sso enforcer

What does this MR do and why?

In !56867 (diffs) we introduced check if user is logged in through SSO for git activity, if group requires that.

This MR adds additional spec for group owners - currently only owners of the group that project is under can bypass this limitation.

As there area may be subject to change, I decided to add specs to document current behaviour.

Screenshots or screen recordings

These are strongly recommended to assist reviewers and reduce the time to merge your change.

How to set up and validate locally

It's only change is specs.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.