Differentiate testing story between partition schedules and cron schedules, relative imports, expand tests
Summary: This diff differentiates between invoking cron schedules and partition schedules. This is necessary because the underlying functions decorated by partition schedules and cron schedules are different (partition schedules take a datetime, cron schedules take a context). Updates testing story to reflect these changes. Additionally expands tests to encompass all schedule examples, and converts imports to relative imports.
Unit and docs build
Reviewers: sandyryza, yuhan
Reviewed By: yuhan
Differential Revision: https://dagster.phacility.com/D8382