Storage rework part 1 (#337)

* Create docs for Integrated Persistent Storage

* add a clear note about possibly moving to PVC's in the (near) future.

* Adapt developer docs to reflect new storage system

* Move Apps fixed-storage to new Storage system

stable/collabora-online/3.0.0/Chart.yaml

@@ -1,7 +1,7 @@
 apiVersion: v2
 kubeVersion: ">=1.16.0-0"
 name: collabora-online
-version: 2.2.2
+version: 3.0.0
 # upstream_version:
 appVersion: "auto"
 description: Collabora Online Development Edition – an awesome, Online Office suite image suitable for home use.