Reduce transactions for writes

[pimeys]

If we only trigger one query for a write operation, we do not need to run it in a transaction, therefore saving two roundtrips from the query. In certain databases, an insert, update or delete query can return the data in the same query. This would cut an insert/update/delete and select combination into a single query. And now when we run only one query, we don't need to run that inside a transaction, saving more roundtrip time.

This would help with pool timeouts, described in #4280

We might need to implement the RETURNING ticket first to reduce the number of queries per write: #5043