Joins multiple distinct PSBTs with different inputs and outputs into one PSBT.
txsarrayREQUIREDcurl --user myuser --data-binary '{"jsonrpc":"1.0","id":"1","method":"joinpsbts","params":[["psbt1","psbt2"]]}' -H 'content-type:text/plain;' http://127.0.0.1:8332/"cHNidP8BAJo...joined..."