4.0.0 release notes: Khepri will be fully supported starting with 4.0

(cherry picked from commit 7da783b)

Author: michaelklishin

release-notes/4.0.0.md

@@ -9,7 +9,8 @@ and those who hold a valid [commercial support license](https://tanzu.vmware.com
 
 Some key improvements in this release are listed below.
 
- * [Khepri](https://www.youtube.com/watch?v=whVqpgvep90), an [alternative schema data store](https://github.com/rabbitmq/rabbitmq-server/pull/7206) developed to replace Mnesia, has matured
+ * [Khepri](https://www.youtube.com/watch?v=whVqpgvep90), an [alternative schema data store](https://github.com/rabbitmq/rabbitmq-server/pull/7206) developed to replace Mnesia,
+   has matured and is now fully supported (it previously was an experimental feature)
  * [AMQP 1.0 is now a core protocol](https://www.rabbitmq.com/blog/2024/08/05/native-amqp) that is always enabled. Its plugin is now a no-op that only exists to simplify upgrades.
  * The AMQP 1.0 implementation is now significantly more efficient: its peak throughput is [more than double than that of 3.13.x](https://www.rabbitmq.com/blog/2024/08/21/amqp-benchmarks)
    on some workloads