What does this PR do?

• Fixes #21050
• /claim #21050

Issue

The core issue is that fetching availability data for Outlook calendars currently involves querying the Microsoft Graph API every time someone views a public booking page that uses an Outlook calendar.

How it was fixed

Used the Google Calendar code as base to implement caching to the Microsoft Graph response and added a webhook to handle calendar change notifications and update the cache.

Also allowed office365_calendar integration to be watched and unwatched on the calendar-cache cronjob.

Next steps

We should refactor some duplicate code between googlecalendar.CalendarService and office365calendar.CalendarService.

Visual Demo (For contributors especially)

https://cap.link/e6g6jgd2t1nztd9

Mandatory Tasks (DO NOT REMOVE)

• I have self-reviewed the code (A decent size PR without self-review might be rejected).
• N/A
• 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?
  • OUTLOOK_WEBHOOK_TOKEN: Token to verify incoming webhooks from Microsoft Outlook (Required)
  • OUTLOOK_WEBHOOK_URL: Optional URL to override for tunelling webhooks. Defaults to NEXT_PUBLIC_WEBAPP_URL.
• What are the minimal test data to have?
  • Setup two or more outlook calendars, create a team on cal.com and enable the calendar-cache feature flag for your team.
• What is expected (happy path) to have (input and output)?
  • If all the above is meet, then:
    1. Go to the public page of one of your events, this should create an entry on SelectedCalendar table
    2. Run the calendar-cache cronjob manually or wait for it to run automatically
    3. The cronjob will subscribe to change notifications
    4. Add, update or delete an event in one of your calendars
    5. The webhook should be called and an entry should be added to CalendarCache table
• Any other important info that could help to test that PR
  • Microsoft Graph requires the webhook callback url to be https

Summary by mrge

Added support for caching Outlook calendar availability and handling Microsoft Graph webhooks to keep cache updated.

• New Features
  • Added webhook endpoint for Outlook calendar event changes.
  • Cached Outlook calendar availability to reduce API calls.
  • Updated database schema to store Outlook subscription info.
  • Extended calendar-cache logic to support Outlook calendars.