chore: EventManager add cancelEvent method

[joeauyeung]

This PR is stacked on #14147. A part of the CRM refactor

What does this PR do?

This PR adds the cancelEvent method to the EventManager class. Logic surrounding deleting 3rd party data when canceling a booking lived in both handleCancelBooking and the EventManager in a private class.

My hope with this PR is to refactor this so this logic only lives inside of the EventManager

Fixes #14451

Requirement/Documentation

• If there is a requirement document, please, share it here.
• If there is a UI/UX design document, please, share it here.

Type of change

• Chore (refactoring code, technical debt, workflow improvements)

How should this be tested?

• Install a calendar and a video integration and enable them on an event type
  • I used GCal and Zoom
• Create a booking
  • The references should be created in the 3rd party apps
• Delete the booking
  • The references should be deleted in the 3rd party apps

Mandatory Tasks

• Make sure you have self-reviewed the code. A decent size PR without self-review might be rejected.

Checklist

• I haven't added tests that prove my fix is effective or that my feature works
• I haven't checked if new and existing unit tests pass locally with my changes

[zomars]

LGTM. Let's wait for the missing check