Use IncidentSeverity in IncidentInfo (Azure#15762)

Co-authored-by: Anat Gilenson <[email protected]>

Author: anat-gilenson

specification/securityinsights/resource-manager/Microsoft.SecurityInsights/preview/2019-01-01-preview/SecurityInsights.json

@@ -7902,40 +7902,8 @@
         },
         "severity": {
           "description": "The severity of the incident",
-          "enum": [
-            "Critical",
-            "High",
-            "Medium",
-            "Low",
-            "Informational"
-          ],
           "type": "string",
-          "x-ms-enum": {
-            "modelAsString": true,
-            "name": "CaseSeverity",
-            "values": [
-              {
-                "description": "Critical severity",
-                "value": "Critical"
-              },
-              {
-                "description": "High severity",
-                "value": "High"
-              },
-              {
-                "description": "Medium severity",
-                "value": "Medium"
-              },
-              {
-                "description": "Low severity",
-                "value": "Low"
-              },
-              {
-                "description": "Informational severity",
-                "value": "Informational"
-              }
-            ]
-          }
+          "$ref": "#/definitions/IncidentSeverity"
         },
         "title": {
           "description": "The title of the incident",