What does this PR do?

This PR implements a calendar cache system for MS Outlook using the MS Graph API.

/claim https://github.com/calcom/cal.com/issues/21050

• feat https://github.com/calcom/cal.com/issues/21050 (Outlook Cache Bounty-to-Hire)

Visual Demo (For contributors especially)

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Video Demo (if applicable):

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Image Demo (if applicable):

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Mandatory Tasks (DO NOT REMOVE)

• I have self-reviewed the code (A decent size PR without self-review might be rejected).
• I have updated the developer docs in /docs if this PR makes changes that would require a documentation change. If N/A, write N/A here and check the checkbox.
• I confirm automated tests are in place that prove my fix is effective or that my feature works.

How should this be tested?

• Are there environment variables that should be set?
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Checklist

• I haven’t read the contributing guide
• My code doesn’t follow the style guidelines of this project
• I haven’t commented my code, particularly in hard-to-understand areas
• I haven’t checked if my changes generate no new warnings

Summary by cubic

Added caching for MS Outlook Calendars using the Microsoft Graph API, with webhook notifications to keep calendar data up to date.

• New Features
  • Implemented a webhook endpoint to receive and process MS Graph notifications.
  • Added database fields and logic to track Office 365 calendar subscriptions and cache expiration.
  • Updated calendar availability logic to use and refresh cache based on webhook events.