event log / instance api for event_records
Summary:
Rather than have the include_cursor flag determine the return value of events_for_asset_key,
introduce a event_records_for_asset_key instance method and document it
Test Plan: bk
Reviewers: yuhan, sandyryza, alangenfeld
Reviewed By: yuhan
Differential Revision: https://dagster.phacility.com/D8610