The previous implementation using Django's `get_or_create` for
`do_increment_logging_stat` involved two separate database queries,
potentially leading to race conditions.
Use an `ON CONFLICT ... DO UPDATE` (aka "upsert") query, which
eliminates race conditions and improves performance. This is mildly
complicated due to the different unique indexes across the various
tables, and the need for bug-for-bug compatibility with the previous
implementation.
Fixes#28947.
Co-authored-by: Alex Vandiver <alexmv@zulip.com>
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