Scheduler tool - Block calendar slots automatically on US holidays

We need to delete the meeting slot on holidays to block scheduling any meeting on holidays. We should be able to automatically block calendar slots on holidays by looking at US holidays in holiday calendar in azuresdk bot's outlook account and remove any slots on holidays.

Start at the Scheduler tool's meeting-slot handling and inspect how it accesses the azuresdk bot's Outlook holiday calendar. Done means US-holiday dates are detected and corresponding meeting slots are blocked or removed so meetings cannot be scheduled on those dates.

Written by the indexing model from the issue text.