add source code and readme

manifests/infrastructure/postgresql/PostgresqlVolumeRestore.md

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+# Recovering a partition from Longhorn Backup volume
+
+## Pull the volume in the longhorn ui
+Under backups, choose which ones to restore (data and wal). Be sure that the replica count is 1, 
+the ReadWrite mode is ReadWriteOne. This should match what you had for the Pg volumes.
+
+Get the volumes onto the same node. You may need to attach them, change the replica count, 
+then delete off of the undesired node.
+
+## Swap the Volume under the PVC
+Put CNPG into hibernate mode and wait for the database nodes to clear.
+
+```yaml
+cluster
+metadata:
+  name: postgres-shared
+  namespace: postgresql-system
+  annotations:
+    # 🔑 CRITICAL: Hibernation prevents startup and data erasure
+    cnpg.io/hibernation: "on"
+spec:
+  instances: 1 # it's way easier to start with one instance
+
+  # put the cluster into single node configuration
+  minSyncReplicas: 0
+  maxSyncReplicas: 0
+```
+
+If you haven't deleted the db cluster you should be able to use the same volume names as the preivous primary.
+If you did, then you'll use postgresql-shared-1 or whatever your naming scheme is. But wait to make them
+until AFTER the initdb runs the first time. If you are starting over, you'll have to set the 
+annotation for `lastGeneratedNode` to 0. 
+`kubectl patch clusters.postgresql.cnpg.io mydb --type=merge --subresource status --patch 'status: {latestGeneratedNode: 0}'` so that it'll create the first instance.
+You'll also want to use a new PVC so that initdb clears out the data and then swap in your volume into that one.
+
+
+Once you're past this stage, put it back into hibernation mode.
+
+(why did I delete the files???)
+
+Anyway, you need to swap the volume out from under the PVC that you're going to use.
+You'll make a new pvc and set the (target?) uuid that identifies the volume to a new value.
+I think this comes from longhorn. Make sure that the volume labels match the names of your recovery volumes.
+
+Then you'll have to make sure that your PVCs are annotated with the same annotations on your previous PVCs 
+since CNPG puts it's own annotations on them. It'll look like the below from https://github.com/cloudnative-pg/cloudnative-pg/issues/5235. Make sure that versions and everything else matches. You need these otherwise the operator won't find a volume to use.
+```yaml
+  annotations:
+    cnpg.io/nodeSerial: "1"
+    cnpg.io/operatorVersion: 1.24.0
+    cnpg.io/pvcStatus: ready
+    pv.kubernetes.io/bind-completed: "yes"
+    pv.kubernetes.io/bound-by-controller: "yes"
+    volume.beta.kubernetes.io/storage-provisioner: driver.longhorn.io
+    volume.kubernetes.io/storage-provisioner: driver.longhorn.io
+  finalizers:
+  - kubernetes.io/pvc-protection
+  labels:
+    cnpg.io/cluster: mydb
+    cnpg.io/instanceName: mydb-1
+    cnpg.io/instanceRole: primary
+    cnpg.io/pvcRole: PG_DATA
+    role: primary
+  name: mydb-1
+  namespace: mydb
+  ownerReferences:
+  - apiVersion: postgresql.cnpg.io/v1
+    controller: true
+    kind: Cluster
+    name: mydb
+    uid: f1111111-111a-111f-111d-11111111111f
+```
+
+### Go out of hibernation mode.
+You should see your pod come up and be functional, without an initdb pod. Check it.
+After a while, scale it back up.