fix(flags): Resolve api_key parameter conflict in remote_config

The post() function automatically sets api_key in the request body,
causing a conflict when we also passed api_key as a kwarg.

Fixed by creating a custom POST request for remote_config that:
- Uses personal_api_key for Authorization header
- Includes project_api_key in request body
- Maintains proper request structure

Author: haacked

posthog/request.py

@@ -139,13 +139,27 @@ def remote_config(
     timeout: int = 15,
 ) -> Any:
     """Get remote config flag value from remote_config API endpoint"""
-    res = post(
-        personal_api_key,
-        host,
-        f"/api/projects/@current/feature_flags/{key}/remote_config/",
-        timeout=timeout,
-        api_key=project_api_key,
-    )
+    import requests
+    from datetime import datetime
+    from dateutil.tz import tzutc
+    
+    url = remove_trailing_slash(host or DEFAULT_HOST) + f"/api/projects/@current/feature_flags/{key}/remote_config/"
+    
+    body = {
+        "api_key": project_api_key,
+        "sentAt": datetime.now(tz=tzutc()).isoformat()
+    }
+    
+    headers = {
+        "Authorization": f"Bearer {personal_api_key}",
+        "Content-Type": "application/json",
+        "User-Agent": USER_AGENT
+    }
+    
+    data = json.dumps(body, cls=DatetimeSerializer)
+    
+    res = requests.post(url, data=data, headers=headers, timeout=timeout)
+    
     return _process_response(
         res,
         success_message=f"POST /api/projects/@current/feature_flags/{key}/remote_config/ completed successfully",