Ability to manage strict group/project members list

Created by: radkomateusz

Hi, I want to submit feature request.

I want to manage whole list of group/project members by single resource as I would like to ensure that terraform configure only given set of members.

Expected behaviour: Resource ensures that only given set of members are configured. If additional members will be added manually, then TF plan/apply will remove them. If members are removed manually, then TF plan/apply will add them again.

Proposed Terraform Configuration Files

resource "gitlab_project_membership_binding" "test" {
  project_id   = "12345"
  user_ids      = [1337, 1338,1372]
  access_level = "maintainer"
}

I want to have similar concept here like in GCP provider (https://www.terraform.io/docs/providers/google/r/google_project_iam.html) - to be able manage: whole policy mapping, only binding for given access level, and also single membership (which is currently the only possible).