Refactor billing code and add error monitoring

Refactored the code that retrieves the billing customer id by renaming the function getBillingCustomerId to getCustomerId. Also, bolstered error handling: implemented exception capture in particular scenarios across multiple files. If an error occurs, it's now captured and reported to the configured provider.

packages/next/package.json

@@ -16,6 +16,7 @@
   "devDependencies": {
     "@kit/auth": "workspace:^",
     "@kit/eslint-config": "workspace:*",
+    "@kit/monitoring": "workspace:*",
     "@kit/prettier-config": "workspace:*",
     "@kit/supabase": "workspace:^",
     "@kit/tailwind-config": "workspace:*",