### What?
This PR updates the `Uploading Files` section in the `Uploads` docs to:
- Use `_payload` in the file upload example, which is required for
non-file fields to be parsed correctly by Payload.
- Add a clear comment explaining that the fields inside `_payload`
should match the schema of the upload-enabled collection.
### Why?
These changes aim to reduce confusion when uploading files via the REST
API.
Fixes#11681
83319be752