Add ability to list users

[gtherond]

Hi team! Could we add a openstack_identity_users_info gauge as similar to what we've got with openstack_identity_projects_info?

We would like to use this information to join it with the nova_servers list and be able to generate a dashboard that shows the following structure for each node on Grafana (Using repeat option):

DUMMYNODE:

ID	NAME	PROJECT	EMAIL
78c8760d-0222-44c7-938b-17a6385e8436	DUMMYVM	DUMMY_TENANT	[email protected]