[v3-0-test] Add note about payload size considerations in API docs (#51732) (#51768)

(cherry picked from commit 69da3f7)

Co-authored-by: Amogh Desai <amoghrajesh1999@gmail.com>

Author: github-actions[bot]

airflow-core/docs/security/api.rst

@@ -93,3 +93,10 @@ Page size limit
 To protect against requests that may lead to application instability, the stable API has a limit of items in response.
 The default is 100 items, but you can change it using ``maximum_page_limit``  option in ``[api]``
 section in the ``airflow.cfg`` file.
+
+Request Payload Considerations
+------------------------------
+
+When using REST APIs that accept data payloads (such as the Variables API), be mindful of the payload size.
+Large payloads (out of ordinary size, like a million bytes) can impact the performance of the Airflow webserver.
+It's recommended to implement appropriate size limits at the proxy layer for your deployment.