Support configuring prometheus fetcher for CloudKitty

Change-Id: I7d79a18599f54583ff4f38a554459fe02ada9ae7

ansible/roles/cloudkitty/templates/cloudkitty.conf.j2

@@ -89,6 +89,19 @@ auth_section = keystone_authtoken
 region_name = {{ openstack_region_name }}
 {% endif %}
 
+{% if cloudkitty_fetcher_backend == "prometheus" %}
+[fetcher_prometheus]
+metric = openstack_identity_project_info
+scope_attribute = id
+prometheus_url = {{ cloudkitty_prometheus_url }}
+
+{% if cloudkitty_prometheus_cafile is defined %}
+cafile = {{ cloudkitty_prometheus_cafile }}
+{% endif %}
+
+insecure = {{ cloudkitty_prometheus_insecure_connections }}
+{% endif %}
+
 [api]
 host_ip = {{ api_interface_address }}
 port = {{ cloudkitty_api_port }}

doc/source/reference/rating/cloudkitty-guide.rst

@@ -59,7 +59,11 @@ CloudKitty natively supports multiple fetcher backends.
 By default Kolla Ansible uses the ``keystone`` backend. This can be changed
 using the ``cloudkitty_fetcher_backend`` option.
 
-You will need to provide extra configuration for non-default fetchers in
+Kolla Ansible also supports the ``prometheus`` backend type, which is
+configured to discover scopes from the ``id`` label of the
+``openstack_identity_project_info`` metric of OpenStack exporter.
+
+You will need to provide extra configuration for unsupported fetchers in
 ``/etc/kolla/config/cloudkitty.conf``.
 
 Cloudkitty Storage Backend