Chain dashboard jon and instance vars

Author: v-zhuravlev

mysqld-mixin/dashboards/mysql-overview.json

@@ -3739,14 +3739,14 @@
           ]
         },
         "datasource": "$datasource",
-        "definition": "label_values(mysql_up, instance)",
+        "definition": "label_values(mysql_up{job=~\"$job\"}, instance)",
         "hide": 0,
         "includeAll": true,
         "label": "instance",
         "multi": true,
         "name": "instance",
         "options": [],
-        "query": "label_values(mysql_up, instance)",
+        "query": "label_values(mysql_up{job=~\"$job\"}, instance)",
         "refresh": 1,
         "regex": "",
         "skipUrlSync": false,