What does this PR do?

Checks for guests for availability, if guest is a cal.com user, when host/organizer is rescheduling the meeting.

• Fixes #16378 (GitHub issue number)
• Fixes CAL-XXXX (Linear issue number - should be visible at the bottom of the GitHub issue description)

/claim #16378

https://www.loom.com/share/bb78a91c2f7a43528fad1eb81cc57ab6?sid=70857687-9d0d-48bd-8d45-0be4a09abd29

Mandatory Tasks (DO NOT REMOVE)

• I have self-reviewed the code (A decent size PR without self-review might be rejected).
• I have added a Docs issue here 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?

• Book a meeting using a cal.com user as the booker.
• Make sure than the booker has some events on his calendar/cal.com account.
• Try to reschedule the above meeting from the host/organizer account.
• Notice that the slots are not shown when the booker is not available.