add traefik middleware template

common/templates/traefik/_middleware.tpl

+# https://doc.traefik.io/traefik/middlewares/overview/
+{{- define "common.traefik.middleware" }}
+apiVersion:  {{ .Values.apiVersion | default "traefik.io/v1alpha1" }}
+kind: Middleware
+metadata:
+  name: {{ .Values.name | default "middleware" }}
+  {{- with .Values.annotations }}
+  annotations:
+    {{- toYaml . | nindent 4 }}
+  {{- end }}
+  labels:
+    {{- include "common.variables.labels" . | nindent 4 }}
+spec:
+  {{- .spec | default .Values.spec | toYaml | nindent 2 }}
+---
+{{- end }}