Create set signal data transaction

Returns a serialized `set_signal_data` transaction, signed with the validator's signing (warm) key. You need to provide the address of a basic account (the sender wallet) to pay the transaction fee. The `new_signal_data` field is interpreted as follows: null = Clear the signal data field (set it to None). \"0x29a4b...\" = Set the signal data field to Some(0x29a4b...). Note: this *replaces the entire signal data field*, overwriting any protocol version previously signaled via `create_signal_version_transaction`. Use that method instead if you only want to update the version while preserving the rest of the signal data. This transaction is only valid from protocol version `upgrades::v2::WARM_KEY_SIGNALING` onwards.