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