Expose HA proxy stats interface

[Graham Burgess]

Currently the charm configures HAProxy stats interface to only listen on localhost. It would be nice to have a config option to expose the interface allowing users to log into and review stats.

[Xav Paice (xavpaice)]

There's an old commit at https://github.com/CanonicalBootStack/charm-openstack-dashboard/pull/1/commits/94d1e086d694d14541c543ca194ad191d81f0c3e which addresses this, but we will need to work on that change in order to make it merge cleanly against master before we can submit that upstream.

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/697708
Committed: https://git.openstack.org/cgit/openstack/charm-openstack-dashboard/commit/?id=8b6d16698aa96133edf0f2ec84f5e12474bcd46f
Submitter: Zuul
Branch: master

commit 8b6d16698aa96133edf0f2ec84f5e12474bcd46f
Author: cjohnston <email address hidden>
Date: Fri Dec 6 18:34:53 2019 +0000

    Add config option for exposing HAProxy stats interface.

    Change-Id: I41799835a4d59dd7d4e0c0becf0908eaab6281ae
    Closes-Bug: #1710208
    func-test-pr: https://github.com/openstack-charmers/zaza-openstack-tests/pull/147