Implement Lemon Squeezy billing services

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.

packages/billing/gateway/src/server/services/billing-event-handler/billing-gateway-factory.service.ts

@@ -16,12 +16,16 @@ export class BillingEventHandlerFactoryService {
         return new StripeWebhookHandlerService();
       }
 
-      case 'paddle': {
-        throw new Error('Paddle is not supported yet');
+      case 'lemon-squeezy': {
+        const { LemonSqueezyWebhookHandlerService } = await import(
+          '@kit/lemon-squeezy'
+        );
+
+        return new LemonSqueezyWebhookHandlerService();
       }
 
-      case 'lemon-squeezy': {
-        throw new Error('Lemon Squeezy is not supported yet');
+      case 'paddle': {
+        throw new Error('Paddle is not supported yet');
       }
 
       default: