nutanix_users_v2 should support import

[jcantrell-ntnx]

Is your feature request related to a problem? Please describe.
Need to bring existing Prism Central users into Terraform state with v2 resource.

Describe the solution you'd like
Add importer for nutanix_users_v2 (ideally for group resources as well).

Describe alternatives you've considered
The existing (v1.x) user resource does support import, but the objective is to move away from the older resources in preparation for the eventual v3 API deprecation and to take advantage of additional capabilities with other v2 resources.

Additional context
Working with a customer on investigating import/migration of v1 provider resources to v2. I've demonstrated success with virtual machines which already support import on the v2 resource, but need to continue working through the list of other deployed resources.