switch from discord to slack webhook (#1476)

Author: LineIndent

pcweb/templates/docpage/state.py

@@ -51,7 +51,7 @@ def handle_submit(self, form_data: dict):
 Score: {"👍" if self.score == 1 else "👎"}
 Feedback: {feedback}
 """
-        payload = {"content": discord_message}
+        payload = {"text": discord_message}
         try:
             with httpx.Client() as client:
                 response: Response = client.post(