Execute rabbitmq post_upgrade hook

Current implementation of rabbitmq-upgrade post_upgrade [1] performs
re-balance of queues between nodes, once upgrade is completed.

Which might be a very reasonable task to execute after any upgrade.

[1] https://www.rabbitmq.com/docs/man/rabbitmq-upgrade.8#post_upgrade

Change-Id: I54b8e22d3c8a3ea797724611f542d9e17982d92c

tasks/main.yml

@@ -114,3 +114,7 @@
         - (_cluster_state.get('running_nodes', []) | length) == (groups[rabbitmq_host_group] | length)
         - (_cluster_state.get('alarms', []) | length) == 0
         - (_cluster_state.get('partitions', []) | length) == 0
+
+    - name: Run rabbitmq post_upgrade hook (rebalance queues)
+      ansible.builtin.command: rabbitmq-upgrade post_upgrade
+      changed_when: false