[contributor] Split user-guides to admin-guide and user-guide
[contributor] Split user-guides to admin-guide and user-guide

After reorganization, we have only two guides as user guides,
I think it is better to use simple naming to avoid confusion.

Change-Id: I756f32251ca7fcde74245c8fb75d4c3069c8f8af

openstack/openstack-manuals,AlekhyaMallina-Vedams/openstack-manuals,AlekhyaMallina-Vedams/openstack-manuals,openstack/openstack-manuals,openstack/openstack-manuals,AlekhyaMallina-Vedams/openstack-manuals,openstack/openstack-manuals