Description of the problem, including code/CLI snippet

It appears that a groups object doesn't have any methods to read or modify push rules

https://docs.gitlab.com/ee/api/groups.html#push-rules

Expected Behavior

Expected similar functionality to the projects.pushrules methods, to be able to read and modify push rules at the group level that projects underneath the group will inherit.

Actual Behavior

No pushrules methods exist in a groups object

Specifications

• python-gitlab version: python-gitlab==2.5.0
• API version you are using (v3/v4): v4
• Gitlab server version (or gitlab.com): gitlab.com