[ADD]pms_downpayment_autoinvoice: ADD module

[DarioLodeiros]

This pull request introduces the new pms_downpayment_autoinvoice module, which automates downpayment invoicing for PMS payments based on configurable company schedules. The changes add all required module files, configuration, and documentation, enabling companies to set up automatic downpayment invoice creation with flexible scheduling (daily, weekly, monthly, quarterly) and batch processing. The module is multi-company aware and includes a daily cron job to trigger the automation.

Automation and scheduling:

• Added data/ir_cron.xml to create a daily cron job (cron_pms_downpayment_autoinvoice) that evaluates and runs the downpayment automation per company according to its schedule.