Server - Billing

[Sv443]

TBD: Use a payment processing framework like Stripe or Lemon Squeezy

• GET /account/{id}/billing/plans to list all plans
• GET /account/{id}/billing to get all billing info for the given account, like current plan and cost per month
• POST /account/{id}/billing/plan to sign up for a plan
• PUT /account/{id}/billing/plan to modify the current plan
• DELETE /account/{id}/billing/plan to cancel the subscription
• GET /account/{id}/billing/invoices to get a list of invoices
• TBD: all other endpoints for managing the actual payment methods