fix: unhandled connection errors

[Quentin-M]

pg-pool requires attaching an error handler to each connection acquired from the pool, which will handle connection-level errors. Without it, the process ends up crashing whenever the connection is interrupted (e.g. database failover).

This fact can be observed in pg-pool:

• newClient 1 and _release (back to the pool) 2 attaches an "idleListener" error handler which upon encountering a connection error, destroys the connection / removes it from the pool, and re-emits 3
• _acquireClient removes the "idleListener", leaving the returned connection without an error handler 4

This PR is in response to production outages we have faced during Aurora PostgreSQL failovers, with the unexpected disconnections for actively-used connections turning error emits into unhandled exceptions and ultimately crashing the entire NodeJS process, despite our existing error handlers on both .on('error' and .adapter.pg.on('error', and our catch-all try/catches.. With this patch in place, the unexpected disconnects (e.g. which could be simulated with a tcpkill -9) no longer crash the processes, proper errors are yielded by the queries - which can then be captured as usual, and the application can eventually recover once the database is available once again.

See brianc/node-postgres#1324 (and more specifically the last few comments there).

Checklist

• DCO (Developer Certificate of Origin) signed in all commits
• Tested as fixing our production outages
• npm test passes on your machine
• New tests added or existing tests modified to cover all changes
• Code conforms with the style guide
• Commit messages are following our guidelines

[dhmlau]

@Quentin-M, thanks for your contribution. Your changes LGTM.

[Quentin-M]

Thank you!

Let me know if you want me to spend the time to fix the commitlint...

✖   body must have leading blank line [body-leading-blank]
✖   subject may not be empty [subject-empty]
✖   type may not be empty [type-empty]

[dhmlau]

@Quentin-M, yes please!

[dhmlau]

@Quentin-M, thanks again for your contribution. Your PR has landed!