Update custom data to support complex objects

[bgervan]

Description

Support complex custom_data like in Product create example on Paddle api doc.

{
  "name": "AeroEdit Student",
  "tax_category": "standard",
  "description": "Essential tools for student pilots to manage flight logs, analyze performance, and plan routes, and ensure compliance. Valid student pilot certificate from the FAA required.",
  "image_url": "https://paddle.s3.amazonaws.com/user/165798/bT1XUOJAQhOUxGs83cbk_pro.png",
  "custom_data": {
    "features": {
      "aircraft_performance": true,
      "compliance_monitoring": false,
      "flight_log_management": true,
      "payment_by_invoice": false,
      "route_planning": true,
      "sso": false
    },
    "suggested_addons": [
      "pro_01h1vjes1y163xfj1rh1tkfb65",
      "pro_01gsz97mq9pa4fkyy0wqenepkz"
    ],
    "upgrade_description": null
  }