Add event.severity_label

salt/elasticsearch/templates/so/so-common-template.json.jinja

@@ -395,6 +395,10 @@
             "severity": {
               "type": "long"
             },
+	    "severity_label": {
+              "ignore_above": 1024,
+              "type": "keyword"
+            },
             "start": {
               "type": "date"
             },