What does this PR do?

Adds an option to skip writing to calendar in the ics-feed app (#13337). This allows it to integrate with calendar services that can’t be written to, like Proton Calendar.

• Fixes #14300
• Fixes CAL-3738

/claim #14300

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
• I have added or modified automated tests that prove my fix is effective or that my feature works (PRs might be rejected if logical changes are not properly tested)

How should this be tested?

• “ICS Feed” can still be installed from the App Store.
• Setup screen with “skip writing to calendar” works.
• Booking an event for a user using the app with the option enabled, works as expected.