Add custom_openstack_server_info and flavor_info metrics

Official OpenStack Exporter has limited server(VM) information. The main reason is to track flavor usage.

custom_openstack_server_info{created="2020-06-12T09:00:00Z",flavor_name="standard.large",image_id="97c8b617-2f82-4ba7-9e4a-4bb5e289acbb",server_id="163b0aac-4333-4b18-888c-e4307248129a",server_name="PV176-server-2",updated="2022-05-22T22:13:57Z"} 1.0

custom_openstack_flavor_info{disabled="False",disk="80",ephemeral="500",flavor_id="b1b4cbfe-ec4f-4958-98e8-43268e516661",flavor_name="hpc.hdn.30core-128ram-ssd-ephem-500",public="False",ram="131072",vcpus="30"} 1.0

openstack_nova_server_status already has some information, they aren't included in the new metric to evade duplicity. They can be joined through server_id