start storing last_materialization event record data
It was kind of a miss to store just the materialization data instead of the event record.
This diff starts storing the full event record, to minimize any extra fetching needed.
I think the full migration path for this table should be pretty straightforward, and can be done
pretty painlessly with 0.12.0. That should remove all the backcompat logic in this diff.
Test Plan: bk
Reviewers: sandyryza, alangenfeld
Reviewed By: alangenfeld
Differential Revision: https://dagster.phacility.com/D7149