What does this PR do?

• Fixes #18947 (GitHub issue number)
• Fixes CAL-5091 (Linear issue number - should be visible at the bottom of the GitHub issue description)

Visual Demo (For contributors especially)

Video Demo (if applicable):

• Show screen recordings of the issue or feature.
• Demonstrate how to reproduce the issue, the behavior before and after the change.

Image Demo (if applicable):

• Add side-by-side screenshots of the original and updated change.
• Highlight any significant change(s).

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?
• What are the minimal test data to have?
• What is expected (happy path) to have (input and output)?
• Any other important info that could help to test that PR

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 mrge

Added support for marking team members as optional guests for event types, allowing them to receive invites without checking their availability.

• New Features
  • Added a setting to select team members as optional guests in the event type advanced settings.
  • Updated calendar integrations to include optional guests as invitees without affecting availability checks.

/claim #18947