Octavia asserts supports-accessible-upgrade

The Octavia team is asserting "assert:supports-accessible-upgrade" tag.

1. Octavia is a component of an OpenStack cloud[1] delivering a
long-lived API[2].
2. Octavia has asserted the "assert:supports-upgrade" tag[3].
3. The upgrade process does not impact the controlled resource via
the documented procedure[4].
4. The grenade gate validates the controlled resource is not impacted
by the upgrade process[5].

[1] https://governance.openstack.org/tc/reference/projects/octavia.html
[2] https://developer.openstack.org/api-ref/load-balancer/v2/index.html
[3] https://review.openstack.org/577967
[4] https://docs.openstack.org/octavia/latest/admin/guides/upgrade.html
[5] https://github.com/openstack/octavia/blob/master/devstack/upgrade/ \
    resources.sh#L89

Depends-On: https://review.openstack.org/577967
Change-Id: Ia34e9816e73b45c7c8504a21ccc0a126f825b185

reference/projects.yaml

@@ -2177,6 +2177,7 @@ octavia:
       tags:
         - stable:follows-policy
         - assert:supports-upgrade
+        - assert:supports-accessible-upgrade
     octavia-dashboard:
       repos:
         - openstack/octavia-dashboard