V1 - Enhanced Billing Subscriptions with PDF Template Fields

Billing Subscriptions now support additional PDF template customization through new fields:

• pdf_invoice_subject: Customize the subject of the billing subscription template
• pdf_description: Add a description to the billing subscription template
• pdf_invoice_free_text: Include custom free text in the billing subscription template

Updated endpoints with new PDF fields:

• Billing Subscriptions
  • Create (request body and response)
  • Update (request body and response)
  • Show (response)
  • List (response)

Example usage when creating or updating a billing subscription:

{
  "billing_subscription": {
    "pdf_invoice_subject": "Billing subscription subject",
    "pdf_description": "Billing subscription description",
    "pdf_invoice_free_text": "Billing subscription free text",
    // ... other billing subscription fields
  }
}