docs: Update mentions of json_success in documentation.

Updates developer and user-facing documentation that references
json_success for the addition of the request argument.

docs/tutorials/life-of-a-request.md

@@ -203,8 +203,13 @@ in a
 with a content type of 'application/json'.
 
 To pass back data from the server to the calling client, in the event of
-a successfully handled request, we use
-`json_success(data=<some python object which can be converted to a JSON string>)`.
+a successfully handled request, we use `json_success(request, data)`.
+
+The request argument is a
+[HTTP request](https://docs.djangoproject.com/en/3.2/ref/request-response/)
+with additional metadata that Zulip associates with the request object.
+The data argument is a python object which can be converted to a JSON string
+and has a default value of an empty python dictionary.
 
 This will result in a JSON string:
 

templates/zerver/api/incoming-webhooks-walkthrough.md

@@ -115,7 +115,7 @@ def api_helloworld_webhook(
     # send the message
     check_send_webhook_message(request, user_profile, topic, body)
 
-    return json_success()
+    return json_success(request)
 ```
 
 The above code imports the required functions and defines the main webhook
@@ -175,7 +175,7 @@ validate the message and do the following:
   message to the owner of the webhook bot.
 
 Finally, we return a 200 http status with a JSON format success message via
-`json_success()`.
+`json_success(request)`.
 
 ## Step 3: Create an API endpoint for the webhook