Add environment_dict_fn argument to ScheduleDefinition
This diff adds a environment_dict_fn parameter to ScheduleDefinition. This can be used instead of the environment_dict parameter, and should be set to a function that returns an environment_dict.
This will help create date partitioned schedules that are based on config.
Test Plan: unit
Reviewers: #ft, schrockn
Reviewed By: #ft, schrockn
Differential Revision: https://dagster.phacility.com/D1307