Add new custom role permissions, allow GET to retrieve MemberRole

[RicePatrick]

This PR adds support for several new custom role permissions. It also resolves an issue where you could previous add or update customer roles, but you would be unable to read them from the API after they were set.

• Update GroupMember to include MemberRole, allowing the GET APIs to retrieve the custom roles

• Add the following new Permissions

  • Admin CI/CD Variables
  • Admin Terraform States
  • Admin Group Members
  • Manage Group Access Tokens
  • Archive Projects
  • Remove Projects

• Fixed typos in the JSON tags for 2 permissions

  • Manage Project Access Tokens (wasn't plural, should have been)
  • Admin Merge Requests (was plural, shouldn't have been)

There is one additional permission in the example JSON I got from the API (admin_push_rules) that I didn't include, because it's not documented in the member roles documentation yet: https://docs.gitlab.com/ee/api/member_roles.html

[RicePatrick]

@svanharmelen - This PR is ready for your review!