List #7777 in 3.12.0 release notes

(cherry picked from commit 15916bfab42aebb28d177448e863dc252c817052)

Author: michaelklishin

release-notes/3.12.0.md

@@ -171,6 +171,13 @@ Release notes are kept under [rabbitmq-server/release-notes](https://github.com/
    rabbitmqctl set_policy at-least-once-dead-lettering ".*" '{"dead-letter-strategy": "at-least-once"}' --apply-to quorum_queues
    ```
 
+ * It is now possible to limit the maximum number of virtual hosts that can be created
+   in the cluster.
+
+   Contributed by @SimonUnge (AWS).
+
+   GitHub issue: [#7777](https://github.com/rabbitmq/rabbitmq-server/issues/7777)
+
  * Nodes with a lot of (non-mirrored) classic queues with v2 storage enabled
    by default (using `classic_queue.default_version = 2`) now boot faster.