Mention that mirror_pids is a alias available as of 3.11.4

Author: michaelklishin

site/ha.md

@@ -240,6 +240,7 @@ It is possible to list queue leader and mirrors using `rabbitmqctl list_queues`.
 example we also display queue policy since it's highly relevant:
 
 <pre class="lang-bash">
+# mirror_pids is a new field alias introduced in RabbitMQ 3.11.4
 rabbitmqctl list_queues name policy pid mirror_pids
 
 # =&gt; Timeout: 60.0 seconds ...
@@ -679,6 +680,7 @@ a common scenario with lazy queues, for example.
 To see mirror status (whether they are synchronised), use:
 
 <pre class="lang-bash">
+# mirror_pids is a new field alias introduced in RabbitMQ 3.11.4
 rabbitmqctl list_queues name mirror_pids synchronised_mirror_pids
 </pre>
 

site/upgrade.md

@@ -514,6 +514,8 @@ Classic mirrored queue replica state can be verified by listing queues in the ma
 <pre class="lang-bash">
 # For queues with non-empty `mirror_pids`, you must have at least one
 # `synchronised_mirror_pids`.
+#
+# Note that mirror_pids is a new field alias introduced in RabbitMQ 3.11.4
 rabbitmqctl -n rabbit@to-be-stopped list_queues --local name mirror_pids synchronised_mirror_pids
 </pre>