Improving UX for ignoring timezone conflicts

Summary:
When there is a new timezone conflict, you will be able to ignore it with a checkbox.
Fix T15349

Preview:

{F343198}

Test Plan: Having a conflicting timezone, click the notification so the usual popup appears. There is a checkbox, leave it checked to ignore the current conflict, uncheck to manually resolve the conflict by selecting one of the available timezones.

Reviewers: O1 Blessed Committers, valerio.bozzolan, avivey

Reviewed By: O1 Blessed Committers, valerio.bozzolan, avivey

Subscribers: speck, waldyrious, avivey, tobiaswiese, valerio.bozzolan, Matthew, Cigaryno

Maniphest Tasks: T15349

Differential Revision: https://we.phorge.it/D25420