TypeScript: Add confirmed reads config

[kim]

Description of Changes

Adds a way to configure the DbConnection to use confirmed reads.

Expected complexity level and risk

1

Testing

Still figuring out...

[kim]

I've been digging around for a way to test this, but it seems like additional URL parameters are added only on a "real" connection object, so it would require an e2e test harness.

If anyone has a better idea, please let me know.

[cloutiertyler]

Very hyped for this! Just want to ask about confirmedReads vs synchronousCommit (i.e. the color of the bikeshed). I'm okay with either, but wanted to ask if it's worth considering the other for the purpose of being closer to Postgres. Presumably for PGWire it will be literally SET synchronous_commit = ON;

[jsdt]

This looks straight-forward enough that I don't think we need to add automated testing in this PR. I would like to make the default be to not specify a value, rather than defaulting to false.

[kim]

the color of the bikeshed

There is a subtle difference, in that Postgres allows to apply synchronous_commit to individual transactions, whereas we apply it to the entire connection.

That is, from the client's perspective, enabling confirmed reads will affect visibility of transactions made by others (note that this is different from the reducer's perspective).

So, re-using the terminology when it's not exactly the same semantics seems like it could cause confusion.
I'd be open to using "consistency level" or something, although that's arguably less concise and even more jargon-y.