Add reminder to remove custom blackbox endpoints

Author: technowhizz

doc/source/operations/upgrading-openstack.rst

@@ -176,6 +176,23 @@ authentication will fail if this configuration is absent. See `upstream
 Keystone change <https://review.opendev.org/c/openstack/keystone/+/833876>`__
 for more details.
 
+Prometheus blackbox exporter endpoints
+--------------------------------------
+
+Endpoints for the blackbox exporter are now templated in the kolla-ansible
+group vars for the cloud. This means that the
+``prometheus_blackbox_exporter_endpoints`` variable can be removed from the
+``kolla/globals.yml`` file and the endpoints will fallback to the ones
+templated in the group vars. Additional endpoints may be added through the
+``prometheus_blackbox_exporter_endpoints_kayobe`` variable. For example:
+
+.. code-block:: yaml
+
+   prometheus_blackbox_exporter_endpoints_kayobe:
+      - endpoints:
+         - "pulp:http_2xx:{{ pulp_url }}/pulp/api/v3/status/"
+      enabled: "{{ seed_pulp_container_enabled | bool }}"
+
 Known issues
 ============