New Resource: azuread_group_without_members

[jackofallops]

This PR introduces a Group resource that omits management and exposure of group members. This resource is intended for use cases where a Group needs to be managed via terraform, but the members of the group are not of concern, typically where the members list is sufficiently large that performance problems are encountered, and/or members are managed by other means.

closes #954 - Since there is no current way to improve the linear performance problem with the List() call, the azuread_group resource cannot be changed to satisfy a performance improvement.

[katbyte]

this might fix #954

[Andrei-Predoiu]

This is something we really need. We don't set members inside the azuread_group resource but the provider still tries to read all the members.

[jackofallops]

as per azuread_group some tests are failing due to a required change on the underlying CI server image.

[katbyte]

LGTM 🍰