[EngSys][EventGrid] enable generation of api doc model (Azure#26148)

apiview needs it as input to generate api reports

Author: jeremymeng

sdk/eventgrid/eventgrid/api-extractor.json

@@ -2,7 +2,7 @@
   "$schema": "https://developer.microsoft.com/json-schemas/api-extractor/v7/api-extractor.schema.json",
   "mainEntryPointFilePath": "types/src/index.d.ts",
   "docModel": {
-    "enabled": false
+    "enabled": true
   },
   "apiReport": {
     "enabled": true,