fix: support PG reconnects

[mattkrick]

Description

fixes #9643

When the DB disconnects, it's nice to reconnect it.
This is a ridiculously hard problem as it turns out:
brianc/node-postgres#1324
brianc/node-postgres#2112

Depending on when & how the disconnect happens, the client may not be aware of it.

For example:

• If PG sends terminating connection due to administrator command then the PG client reports the error Connection terminated unexpectedly and the app gets killed. I think it gets killed because it's a ProcessInterrupts routine coming from postgres.c and the severity is FATAL.
• If PG sends the database system is shutting down then it reconnects just as expected. This is what we've seen coming from Google CloudSQL.
• The driver also does not throw an error if a first connection hasn't happened, this is because the error event comes from a single connection, so if no connection is made, it can't emit that event, we just get econnrefused. I'm ignoring this case in this PR.

Demo

start up the embedder & then kill the PG container in docker. sometimes you get case 1, sometimes case 2.