Add Slack reminders with current Grant status report

[estyxx]

Implement a functionality to automatically send Slack reminders that provide a quick state-of-the-art summary of the grants. The reminder should aggregate and display counts for various statuses, such as:

• pending
• x confirmed
• x approved
• x waiting for confirmation
• x waiting
• x rejected

In addition, include metrics such as the number of people who have requested accommodation. These messages should be scheduled to run between the grants deadline and the conference start date.

This will be useful for administrators to take necessary actions.