fix(postgres): prevent crash if postgres connection emit multiple errors

[Hackatosh]

Pull Request Checklist

• Have you added new tests to prevent regressions?
• If a documentation update is necessary, have you opened a PR to the documentation repository?
• Did you update the typescript typings accordingly (if applicable)?
• Does the description below contain a link to an existing issue (Closes #[issue]) or a description of the issue you are solving?
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Description Of Change

We recently observed multiple crashes due to an unhandled "server conn crashed?" exception originating from the pg library. As best as I've been able to tell, this shouldn't be possible and should have been fixed in this previous PR : #14731

I think that an error might be able to slip up during the connection without the error listener being properly attached or that error can be fired multiple times and is only handled once.
My fix is to attach the listener before trying to connect to the database. Also I change back the .once handler to a .on (this was changed in the PR 14731) to be able to catch multiple errors.

Todos

[Hackatosh]

PR for version 6 : #15868

[evanrittenhouse]

LGTM - will wait for @ephys or @WikiRik to confirm, since they may have additional insight into to the Postgres error emission logic

[WikiRik]

Suggestion to make the casing of the type a bit nicer

[Hackatosh]

Thanks for your input @WikiRik, I have updated the PR

[WikiRik]

Looks good to me, but I'll give @ephys some time to look at the typing change before I merge

[Hackatosh]

Hello ! Any news on this PR ? @WikiRik @ephys