nick/fix assistant api url (#912)

* Refactor API endpoint to generate assistant messages with updated request and response structures

* Add Mintlify documentation and update API reference for assistant message generation

* Update OpenAPI specification for assistant message generation with new request structure and additional properties

* Add default values for threadId and messages in assistant message generation

* Add back the create topic and generate message pages

* fix: correct the openapi url for assistant

Author: skeptrunedev

discovery-openapi.json

@@ -7,7 +7,7 @@
   },
   "servers": [
     {
-      "url": "https://api-dsc.mintlify.com/api/discovery/v1"
+      "url": "https://api-dsc.mintlify.com/v1"
     }
   ],
   "security": [