fix: Ensure Postgres queries are committed or autocommit is used

[TomSteenbergen]

What this PR does / why we need it:

We are using psycopg3 in case we use Postgres for the online store. If you create connections with psycopg3 using a context manager (i.e. a with ... block), it will automatically commit the transaction once you exit the context. However, in feast we are manually creating (and in the case of connection pools, putting) connections, so we need to ensure that we also explicitly call commit after firing queries to the database.

The commit statements were missing for (async) read methods of the PostgresOnlineStore and the teardown method. For the read statements, this wasn't an issue as we just do a SELECT. However, it does add warning statements and quite a bit of latency as transactions needed to be rolled back.

Hence, for those read methods, I introduced an optional autocommit to the _get_conn and _get_conn_async methods that defaults to False. We are setting it to True in our read methods, so that prevents us from having to call commit and further optimizes the performance. In my local tests, online_read_async performance improved by 20-30% when calling explicitly commit, and 40-70% when enabling autocommit (depending on feature view).

Which issue(s) this PR fixes:

Fixes #5038

[franciscojavierarceo]

Thank you for this!