Implement action for listing routers and their statuses on a unit

[Edin S]

This is required to progress work on juju verify (bug LP#1916231).

As per the above ticket:
neutron-gateway needs an action implemented: get-status-routers
Returns the list of routers running on the unit, and their status

[Edin S (exsdev)]

MR: https://review.opendev.org/c/openstack/charm-neutron-gateway/+/782896

[Aurelien Lourot (aurelien-lourot)]

Added charm-guide as affected project for the release notes.

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/c/openstack/charm-neutron-gateway/+/782896
Committed: https://opendev.org/openstack/charm-neutron-gateway/commit/c6f970673b00b76e54356df4de0d489494449ebb
Submitter: "Zuul (22348)"
Branch: master

commit c6f970673b00b76e54356df4de0d489494449ebb
Author: Edin Sarajlic <email address hidden>
Date: Thu Mar 25 04:17:03 2021 +0000

    Actions that expose various neutron resources

    New actions:
      * show-routers
      * show-dhcp-networks
      * show-loadbalancers

    Partial-Bug: #1916231
    Closes-Bug: #1917401
    Closes-Bug: #1917403
    Closes-Bug: #1917405

    Change-Id: Ie59c2a7d5c1ee9c51a0f7db4e8f38229812ac84a
    func-test-pr: https://github.com/openstack-charmers/zaza-openstack-tests/pull/611