feat: implement billing system with Pally integration

- Added billing models and repository for handling bills.
- Introduced BillingService to manage payment initiation and bill creation.
- Updated user service to remove ticket-related functionality.
- Refactored settings to include new billing-related fields.
- Removed ticket-related handlers and schemas.
- Added new billing handlers for processing payments.
- Updated database schema with new bills table and status enum.
- Enhanced utility functions to calculate prices considering discounts.
- Introduced prehandling for non-private messages.
- Updated main application to initialize new billing services and repositories.

.env.example

@@ -2,10 +2,6 @@
 # Get it from @BotFather on Telegram
 BOT_TOKEN=your_bot_token_here
 
-# Telegram Admin Group ID (Required)
-# The numeric ID of the group where admin notifications will be sent
-ADMIN_GROUP_ID=your_admin_group_id_here
-
 # Remnawave Configuration (Required)
 REMNAWAVE_URL=https://your-remnawave-instance.com
 REMNAWAVE_TOKEN=your_remnawave_api_token_here