Implement Recurring Billing

[AArchange]

Description: Add support for recurring billing for subscriptions and other services.

Tasks:
Modify the Invoice model to handle recurring invoices.
Create a UI to set recurrence intervals (e.g., monthly, yearly).
Automate the generation of recurring invoices.
Acceptance Criteria:
Users can set up recurring billing schedules.
Recurring invoices are automatically generated based on the schedule.