add support for optional configmaps/secrets

library/common/templates/lib/pod/volumes/_configmap.tpl

@@ -20,7 +20,7 @@ objectData: The object data to be used to render the volume.
 
   {{- if $expandName -}}
     {{- $object := (get $rootCtx.Values.configmap $objectName) -}}
-    {{- if not $object -}}
+    {{- if and ( not $object ) ( not $objectData.optional ) -}}
       {{- fail (printf "Persistence - Expected configmap [%s] defined in <objectName> to exist" $objectName) -}}
     {{- end -}}
 
@@ -46,6 +46,9 @@ objectData: The object data to be used to render the volume.
     {{- with $defMode }}
     defaultMode: {{ . }}
     {{- end -}}
+    {{- if $objectData.optional }}
+    optional: true
+    {{- end -}}
     {{- with $objectData.items }}
     items:
       {{- range . -}}