debug: allow intake payload to be dumped to disk when debugging
debug: allow intake payload to be dumped to disk when debugging

Set the enviroment variable `OPBEAT_DEBUG_PAYLOAD=1` to enable.

If enabled, data sent to the Opbeat intake API will be stored as JSON
documents in your operating systems temp directory.

Enable debug mode to see the names of the files being written to disk.

opbeat/opbeat-node,opbeat/opbeat-node