Support for storage class name in kubectl plugin

Added an option to specify the storage class name in 'create' command.
This is useful in environments without a default storage class.

bin/kubectl-rabbitmq

@@ -34,6 +34,7 @@ usage() {
     echo
     echo "  Create a RabbitMQ custom resource - INSTANCE name required, all other flags optional"
     echo "    kubectl rabbitmq create INSTANCE --replicas 1 --service ClusterIP --image rabbitmq:3.8.8 --image-pull-secret mysecret"
+    echo "      --tls-secret secret-name --storage-class mystorageclass"
     echo
     echo "  Get a RabbitMQ custom resource and dependant objects"
     echo "    kubectl rabbitmq get INSTANCE"
@@ -150,6 +151,12 @@ create() {
             echo "    secretName: $1" >>"$rabbitmq_manifest_file"
             shift 1
             ;;
+        "--storage-class")
+            shift 1
+            echo "  persistence:" >>"$rabbitmq_manifest_file"
+            echo "    storageClassName: $1" >>"$rabbitmq_manifest_file"
+            shift 1
+            ;;
         *)
             # Unrecognised or unsupported option
             echo "Option '$1' not recongnised"