Merge pull request #7670 from rabbitmq/mk-update-3.12.0-release-notes-again

More 3.12.0 release notes updates

Author: michaelklishin

release-notes/3.12.0.md

@@ -9,6 +9,7 @@ This release includes several new features and optimizations and graduates (make
 The user-facing areas that have seen the biggest improvements in this release are
 
  * Lower MQTT and Web MQTT memory footprint per connection
+ * Reduced quorum queue memory footprint, improved throughput stability under load
  * Classic queue message store memory efficiency and footprint predictability
  * OAuth 2, OIDC, IDP support
 
@@ -140,7 +141,18 @@ in the `3.11.x` release series.
 
    GitHub issues: [#7443](https://github.com/rabbitmq/rabbitmq-server/pull/7443)
 
- * There is now a way to pre-configure user permissions for newly created virtual hosts.
+ * There is now a way to pre-configure users and their permissions for newly created virtual hosts:
+
+  ``` ini
+  default_users.qa_user.vhost_pattern = qa.*
+  default_users.qa_user.tags = policymaker,monitoring
+  default_users.qa_user.password = fd237824441a78cd922410af4b83f0888186a8d7
+  default_users.qa_user.read = .*
+  default_users.qa_user.write = .*
+  default_users.qa_user.configure = .*
+  ```
+   This is primarily useful in environments where RabbitMQ is provided as a service but
+   customers (clients) have control over virtual hosts.
 
    Contributed by @illotum (AWS).