Additional volumes capability (#736)

* Allow additional Volumes to be mounted

* added TargetContainers option to determine if additional volume need to be mounter or not

* fixed dependencies

* updated manifest additional volume example

* More validation

Check that there are no volume mount path clashes or "all" vs ["a", "b"]
mixtures. Also change the default behaviour to mount to "postgres"
container.

* More documentation / example about additional volumes

* Revert go.sum and go.mod from origin/master

* Declare addictionalVolume specs in CRDs

* fixed k8sres after rebase

* resolv conflict

Co-authored-by: Dmitrii Dolgov <9erthalion6@gmail.com>
Co-authored-by: Thierry <thierry@malt.com>

manifests/complete-postgres-manifest.yaml

@@ -12,6 +12,29 @@ spec:
   volume:
     size: 1Gi
 #    storageClass: my-sc
+  additionalVolumes:
+    - name: data
+      mountPath: /home/postgres/pgdata/partitions
+      targetContainers:
+        - postgres
+      volumeSource:
+        PersistentVolumeClaim:
+          claimName: pvc-postgresql-data-partitions
+          readyOnly: false
+    - name: conf
+      mountPath: /etc/telegraf
+      subPath: telegraf.conf
+      targetContainers:
+        - telegraf-sidecar
+      volumeSource:
+        configMap:
+          name: my-config-map
+    - name: empty
+      mountPath: /opt/empty
+      targetContainers:
+        - all
+      volumeSource:
+        emptyDir: {}
   numberOfInstances: 2
   users:  # Application/Robot users
     zalando: