Add wallet balance to User model and implement Atoll/Island management

- Added `wallet_balance` field to the User model.
- Updated UserAdmin to include `wallet_balance` in the admin interface.
- Created serializers and views for Atoll and Island management.
- Implemented endpoints for listing, creating, and updating Atolls and Islands.
- Enhanced payment processing with UUIDs for Payment and Topup models.
- Added migration files for new fields and constraints.
- Improved error handling and validation in various views.
- Updated email templates for better responsiveness and SEO.

apibase/urls.py

@@ -36,7 +36,8 @@ urlpatterns = [
     path("api/auth/", include("api.urls")),
     # Devices
     path("api/devices/", include("devices.urls")),
-
+    # Billing
+    path("api/billing/", include("billing.urls")),
 ]
 if settings.DEBUG:
     urlpatterns += static(settings.MEDIA_URL, document_root=settings.MEDIA_ROOT)