Update docs with new location of group push rules

What does this MR do and why?

Documents the changes of #220365 (closed)

Screenshots or screen recordings

How to set up and validate locally

See http://gdk.test:3005/ee/user/group/access_and_permissions.html (or use the deployed Review app).

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.