Test and monitor performance regressions

[denismerigoux]

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Prompted by #516, we should have some performance monitoring under CI to detect early performance drops introduced by compiler changes. The interpretation time is the most critical thing to watch.

[AltGr]

One approach could be to use https://github.com/ocurrent/current-bench

Then you get an output looking like https://autumn.ocamllabs.io/ocaml/opam/branch/master?worker=autumn&image=bench.Dockerfile

It seems fairly simple to use if look at https://github.com/ocaml/opam/pull/5574/files

[denismerigoux]

I'm ok for using this!