Add support for building the proxysql image

This should have been added when proxysql was added to kolla [1] and
kolla-ansible [2].

ProxySQL is disabled by default in this change to allow backports. It
will be enabled in a follow-up patch only for the master branch.

[1] https://review.opendev.org/c/openstack/kolla/+/769385
[2] https://review.opendev.org/c/openstack/kolla-ansible/+/770215

Change-Id: I683b685bf4e2f625144e4656bcd69c03eda7aa51

ansible/inventory/group_vars/all/kolla

@@ -231,6 +231,8 @@ overcloud_container_image_regex_map:
     enabled: "{{ kolla_enable_placement | bool }}"
   - regex: ^prometheus
     enabled: "{{ kolla_enable_prometheus | bool }}"
+  - regex: ^proxysql
+    enabled: "{{ kolla_enable_proxysql | bool }}"
   - regex: ^qdrouterd
     enabled: "{{ kolla_enable_qdrouterd | bool }}"
   - regex: ^rabbitmq
@@ -508,6 +510,7 @@ kolla_enable_mariadb: "yes"
 kolla_enable_memcached: "yes"
 kolla_enable_neutron: "{{ kolla_enable_openstack_core | bool }}"
 kolla_enable_nova: "{{ kolla_enable_openstack_core | bool }}"
+kolla_enable_proxysql: "no"
 kolla_enable_rabbitmq: "yes"
 
 # OpenStack services can be enabled or disabled with these options

releasenotes/notes/build-proxysql-image-ec09332ef0b7dae0.yaml

+---
+fixes:
+  - |
+    The ``proxysql`` image is now built when ``kolla_enable_proxysql`` is set
+    to ``true``.