Added implementation for various billing services with Lemon Squeezy. This includes processing of webhooks for order and subscription handling, verification of webhook signatures, and validating subscription statuses and order states. Additionally, types for order and subscription webhooks have been created.
New README files have been added for the packages dealing with the Stripe and Lemon Squeezy billing systems. They explain the purpose of the packages and detail what environment variables need to be set for development and production.