Created a new package named billing-gateway which implements interfaces for different billing providers and provides a centralized service for payments. This will potentially help to maintain cleaner code by reducing direct dependencies on specific payment providers in the core application code. Additionally, made adjustments in existing services, like Stripe, to comply with this change. The relevant interfaces and types have been exported and imported accordingly.
Added README.md files for several @kit packages including Supabase, UI, Emails, Billing, and Mailers. These documents explain the purpose and usage of each package, facilitating better understanding for developers interacting with them.
