Description of the problem, including code/CLI snippet

Gitlab has recently enriched their APIs, especially with respect to Groups. The GroupProjectManager should be updated with the newly available filters. I'm sure that there are more APIs that have been updated.

https://docs.gitlab.com/ce/api/groups.html#list-a-groups-projects
https://github.com/python-gitlab/python-gitlab/blob/master/gitlab/v4/objects.py#L847

Expected Behavior

The ability to use the new filters, specifically include_subgroups

Actual Behavior

CLI errors out stating the parameter is not valid.

Specifications

• python-gitlab version: 1.7.0
• API version you are using (v3/v4): v4
• Gitlab server version (or gitlab.com): 11.6.5-ee