Add lockfile for main

[maiste]

This is a Proof-Of-Concept as it relies on a patch (thanks to @TheLortex) while waiting for this avsm/ocaml-yaml#41 to be merged.

With dune.3.0 and the PR included, we will be able to provide a viable opam monorepo lock file.

To test this PR:

$ git clone https://github.com/maiste/irmin.git
$ git checkout maiste@lockfile
$ opam switch create . --empty
$ eval $(opam env)
$ opam monorepo pull

[codecov-commenter]

Codecov Report

Merging #1774 (ffbea06) into main (679343f) will increase coverage by 0.00%.
The diff coverage is n/a.

❗ Current head ffbea06 differs from pull request most recent head b3fca52. Consider uploading reports for the commit b3fca52 to get more accurate results

@@           Coverage Diff           @@
##             main    #1774   +/-   ##
=======================================
  Coverage   64.53%   64.54%           
=======================================
  Files         115      115           
  Lines       14057    14057           
=======================================
+ Hits         9072     9073    +1     
+ Misses       4985     4984    -1     

Impacted Files	Coverage Δ
src/irmin-unix/fs.ml	67.74% <0.00%> (-0.65%)	⬇️
src/irmin-test/store.ml	95.10% <0.00%> (+0.05%)	⬆️
src/irmin/store.ml	64.67% <0.00%> (+0.14%)	⬆️

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[craigfe]

@maiste: you may find that you need to add (vendored_dirs duniverse) to a top-level dune file to get the CI to pass, as otherwise I think the monorepo universe will be built and tested as if it were part of the Irmin source.

[maiste]

Thanks! Indeed, it would be bad if we test the entire duniverse we are importing....

[maiste]

After discussion, we are going to wait opam-monorepo overlays packages port to dune.3 before considering this PR.

[maiste]

As this lockfile is not up to date anymore this PR can be closed.