Implement audit log for Grants actions

[estyxx]

Implement an audit log for all significant actions related to grants. This will allow us to track changes in grant status and actions like sending emails or generating vouchers. The goal is to maintain a detailed record of what happened and who performed each action.

• [ ] Use the existing utility in custom_admin/audit.py (create_change_admin_log_entry) to log changes.
• [ ] Log an audit entry every time a grant's status changes.
• [ ] Log an audit entry for key actions, such as sending emails or generating vouchers.
• [ ] Ensure all relevant actions are consistently logged to maintain a complete history.