implement excludeFromBackup for volumes

@jan-eike.schnabel this MR now implements the option to exclude a volume from the backup system. Volumes that should be included in the backup get an excludeFromBackup: true label.

I will let you know if this has been implemented for the cosyna-opendap project

{{cookiecutter.project_slug}}/templates/{{cookiecutter.template_base_name}}/persistentvolumeclaim.yaml

@@ -9,6 +9,11 @@ metadata:
   labels:
     {{ "{{-" }} include "{{ cookiecutter.template_base_name }}.labels" . | nindent 4 {{ "}}" }}
     io.kompose.service: {% raw %}{{ .Values.baseName }}{% endraw %}
+    {%- raw %}
+    {{- if .Values.volumeExcludeFromBackup }}
+    excludeFromBackup: true
+    {{- end }}
+    {%- endraw %}
   name: {% raw %}{{ .Values.baseName }}{% endraw %}
   annotations:
     "helm.sh/resource-policy": keep