add support for custom_data

[andrewkoltsov]

Description

paddle announced custom_data as successor to the existing passthrough parameter https://developer.paddle.com/changelog/e9a54055ea46e-custom-data-now-available

Could you please add support for it? FYI: https://developer.paddle.com/changelog/63508dbef06e9-custom-data-returned-as-a-json-encoded-string

thank you