Docs: Add Custom Payload Text for Webhooks (#4248)

* Docs: Add Custom Payload Text for Webhooks

* Update src/docs/product/integrations/integration-platform/webhooks.mdx

Co-authored-by: Isabel <76437239+imatwawana@users.noreply.github.com>

Co-authored-by: Isabel <76437239+imatwawana@users.noreply.github.com>

Author: t-h-man

src/docs/product/integrations/integration-platform/webhooks.mdx

@@ -109,6 +109,11 @@ actor
       'name': 'Sentry',
     },
 ```
+<Note>
+
+You cannot set up a custom payload. Instead, we suggest setting up a server/service that proxies our webhook into a request that fits your use case.
+
+</Note>
 
 ## Event Types