added categories to poi in search.json (Azure#17446)

Author: khmic5

specification/maps/data-plane/Search/preview/1.0/search.json

@@ -2195,6 +2195,14 @@
             "$ref": "#/definitions/PointOfInterestCategorySet"
           }
         },
+        "categories": {
+          "description": "Categories array",
+          "type": "array",
+          "readOnly": true,
+          "items": {
+            "type": "string"
+          }
+        },
         "classifications": {
           "description": "Classification array",
           "type": "array",