Plan for Dune 3.0

[BikalGurung]

@jeremiedimino

However, there is on-going work to add support for OCAMLPATH in the compiler and eventually deprecate ocamlfind . So moving from using OCAMLPATH to using findlib.conf feels like going backward.

@EduardoRFS see in particular this comment. Defining standard OCaml development lifecycle processes - #15 by dbuenzli