The ProxySQL startup script was incorrectly using
the `--reload` flag, which only reloads/merges the configuration
without initializing the database from the config file [1]. This
change corrects it to use the `--initial` flag, ensuring that
the database is always reloaded from the configuration at startup.

[1] https://proxysql.com/documentation/configuring-proxysql/#initialstartup

Change-Id: I9cc721555a6d19409b6ac24432b6b34a83efc42c

The --reload parameter ensures that any changes
in the proxysql configuration file are applied
to the already existing internal proxysql database.

Change-Id: I9215d6cef3795030676c44a8184d99ba46dcb60c

Kolla environment currently uses haproxy
to fullfill HA in mariadb. This patch
is switching haproxy to proxysql if enabled.

This patch is also replacing mariadb's user
'haproxy' with user 'monitor'. This replacement
has two reasons:
  - Use better name to "monitor" galera claster
    as there are two services using this user
    (HAProxy, ProxySQL)
  - Set password for monitor user as it's
    always better to use password then not use.
    Previous haproxy user didn't use password
    as it was historically not possible with
    haproxy and mariadb-clustercheck wasn't
    implemented.

Depends-On: https://review.opendev.org/c/openstack/kolla/+/769385
Depends-On: https://review.opendev.org/c/openstack/kolla/+/765781
Depends-On: https://review.opendev.org/c/openstack/kolla/+/850656

Change-Id: I0edae33d982c2e3f3b5f34b3d5ad07a431162844