OpenTelemetry integration tracking issue

[develop7]

An umbrella issue for tracking of OpenTelemetry integration to PostgREST.

• Get familiar with OTel and terminology
  • Wrap meaningful and measurable actions with OTel spans
• Get hands dirty by exposing Server-Timing metrics for collection (per the suggestion at Feature Request: metrics or instrumentation #1526 (comment))
• Collect metrics during loadtest and include these to reports
• Collect & export memory stats
• Collect web request/response stats with hs-opentelemetry-instrumentation-wai
• Wrap hasql to a stats-collecting middleware

[mkleczek]

I have played with the idea some time ago and have a preliminary implementation.
The main goal was to trace SQL statements so it required Hasql adjustments. I also wanted to play with https://hackage.haskell.org/package/effectful to make the whole thing extensible.

As Hasql is a family of projects I had to fork quite a bunch of Hasql repositories.

At the end of the day only minimal changes to Postgrest itself were needed as I was able to replace monomorphic usage of Hasql with polymorphic based on effectful by using Cabal mixins.

Not sure if there is anything interesting there to actually provide a pull request but maybe worth looking at and discussing.

main...mkleczek:postgrest:temp-opentelemetry

[develop7]

@mkleczek whoa, you've got yourself a nice flake.nix too! Seems to be way ahead of #3105 of mine (and working, I presume?). Do you mind us borrowing a thing here and there, or, better yet, you submit a PR with it?

[mkleczek]

It was working last time I tried :)

As mentioned in #3105 (comment) - static binary builds not tested.