Add changelog to note that 3.0.0 drops all existing data (#18819)

stable/influxdb/Chart.yaml

 apiVersion: v1
 name: influxdb
-version: 3.0.0
+version: 3.0.1
 appVersion: 1.7.6
 description: Scalable datastore for metrics, events, and real-time analytics.
 keywords:

stable/influxdb/README.md

@@ -90,3 +90,7 @@ Values `.Values.config.bind_address` and `.Values.exposeRpc` no longer exist. Th
 ### From < 1.5.0 to >= 2.0.0
 
 The Kubernetes API change to support 1.160 may not be backwards compatible and may require the chare to be uninstalled in order to upgrade.  See [this issue](https://github.com/helm/helm/issues/6583) for some background.
+
+### From < 3.0.0 to >= 3.0.0
+
+Since version 3.0.0 this chart uses a StatefulSet instead of a Deployment. As part of this update the existing persistent volume (and all data) is deleted and a new one is created. Make sure to backup and restore the data manually.