chore(deps): update mysql docker tag to v5.7

kubernetes/templates/cm-and-secrets/mysql-deploy.yml

@@ -13,7 +13,7 @@ spec:
         app: mysql
     spec:
       containers:
-      - image: mysql:5.6
+      - image: mysql:5.7
         name: mysql
         env:
         - name: MYSQL_ROOT_PASSWORD