Document data layout change in RabbitMQ 7.0.0 (#11461)

See: https://github.com/bitnami/charts/issues/10913

Signed-off-by: Talia Wong <blowfishpro@users.noreply.github.com>

bitnami/rabbitmq/README.md

@@ -647,6 +647,12 @@ See the [Upgrading guide](https://www.rabbitmq.com/upgrade.html) and the [Rabbit
 - Chart labels and Ingress configuration were adapted to follow the Helm charts best practices.
 - Initialization logic now relies on the container.
 - This version introduces `bitnami/common`, a [library chart](https://helm.sh/docs/topics/library_charts/#helm) as a dependency. More documentation about this new utility could be found [here](https://github.com/bitnami/charts/tree/master/bitnami/common#bitnami-common-library-chart). Please, make sure that you have updated the chart dependencies before executing any upgrade.
+- The layout of the persistent volumes has changed (if using persistence). Action is required if preserving data through the upgrade is desired:
+  - The data has moved from `mnesia/` within the persistent volume to the root of the persistent volume
+  - The `config/` and `schema/` directories within the persistent volume are no longer used
+  - An init container can be used to move and clean up the peristent volumes. An example can be found [here](https://github.com/bitnami/charts/issues/10913#issuecomment-1169619513).
+  - Alternately the value `persistence.subPath` can be overridden to be `mnesia` so that the directory layout is consistent with what it was previously.
+    - Note however that this will leave the unused `config/` and `schema/` directories within the peristent volume forever.
 
 Consequences: