Sets up migrations for run_storage, to be run upon dagster instance migrate.
Currently, we have a CLI command dagster instance migrate which performs schema migrations, and dagster instance reindex which performs optional data migrations (over the event log).
https://dagster.phacility.com/D5840 adds a partition column to the runs table, which would require a data migration in order to begin doing reads off of that column.
This diff sets up the machinery to track that migration status, and also notably performs a data migration over the runs table upon dagster instance migrate.
The upside is that with 0.10.0, we have some schema changes that must be performed and so we know that people will run dagster instance migrate. The downside is that this is definitely a data migration and its latency depends on the size of the runs table.