Fix mail template charset issue

mail/openeuler.org/mailcore.yaml

@@ -42,6 +42,14 @@ spec:
               value: http://mailman-web-service.mail.svc.cluster.local:8000/hyperkitty
             - name: SMTP_HOST
               value: mailman-exim4-service.mail.svc.cluster.local
+          # Sed command is used here to force change default charsets to UTF-8
+          # related issue: https://gitlab.com/mailman/postorius/issues/325
+          command:
+            - /bin/sh
+            - -c
+            - |
+              sed -i "s/charset: us-ascii/charset: utf-8/g" /usr/lib/python3.6/site-packages/mailman/config/schema.cfg;
+              exec docker-entrypoint.sh master --force
       #NOTE: Empty dir can't be used in a production dir. Please upgrade it before using.
       volumes:
         - name: mailman-core-volume