Implement the persistence layer changes following #19191.
This PR handles writing and reading stats to the new stream stat_table and columns in the existing sync_stats table.
At the same time we introduce upserts of stats records - i.e. merge updates into a single record - in preparation for real time stats updates vs the current approach where a new stat record is always written.
There will be two remaining PRs after this:
- First PR will be to fully wire up and test the API.
- Second PR will be to actually save stats while jobs are running.
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