Backwards compatbility with respect to system timezone between the cron schedulers and the daemon schedulers
Firstly, in cron-based schedulers, only allow schedules with execution_timezone set where the system timezone matches the timezone on the schedule
Before, we were allowing all schedules, but potentially just executing in the wrong timezone, which isn't great. Now, we will not execute the schedule if we can't do it in the right timezone, and tell you why.
This allows us to return the system timezone over graphql as the execution timezone for schedules without timezones explicitly set. Then in 0.11.0 we can require execution timezones to be set for all schedules, remove the cron schedulers, and not worry aboutwhat the system timezone is ever again.
Test Plan: New BK coverage
Reviewers: prha, alangenfeld, schrockn
Reviewed By: prha
Differential Revision: https://dagster.phacility.com/D5438