Lower bound check DYI

From https://github.com/ocaml/opam-repository/pull/19149

The best we know how to do properly at the moment without taking too much time is to do it step by step (same as our CI does currently).

You can use opam-devel.2.1.0 compiled with the opam-0install-cudf package or use it from the ocaml/opam docker images (the opam-2.1 binary already has everything ready):

$ opam install --solver=builtin-0install "--criteria=+count[version-lag,solution]" your-pkg