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.

billing/admin.py

@@ -1,3 +1,13 @@
 from django.contrib import admin
+from .models import Payment, BillFormula, Topup
 
 # Register your models here.
+
+
+class PaymentAdmin(admin.ModelAdmin):
+    list_display = ("id", "user", "amount", "paid", "paid_at", "method")
+
+
+admin.site.register(Payment, PaymentAdmin)
+admin.site.register(BillFormula)
+admin.site.register(Topup)