docs: Make update-message-flags use curl example system.

templates/zerver/api/update-message-flags.md

@@ -44,13 +44,7 @@ zulip(config).then((client) => {
 
 {tab|curl}
 
-``` curl
-curl -X POST {{ api_url }}/v1/messages/flags \
-    -u BOT_EMAIL_ADDRESS:BOT_API_KEY \
-    -d "messages=[4,8,15]" \
-    -d "op=add" \
-    -d "flag=starred"
-```
+{generate_code_example(curl)|/messages/flags:post|example}
 
 {end_tabs}
 

zerver/openapi/test_curl_examples.py

@@ -24,6 +24,7 @@ exclude_list = [
     'update-message.md',
     'delete-message.md',
     'get-message-history.md',
+    'update-message-flags.md',
 ]
 
 def test_generated_curl_examples_for_success(client: Client) -> None: