Publish ocaml.org as an opam package

[cuihtlauac]

ocaml.org is not meant to be used as a package by any other project. However, exposing it as an opam package has some value:

• Makes ocaml.org part of the reverse dependencies non regression checks performed when a package version is published.
• Allows to dev team to have its own package to display in ocaml.org
• Enable testing and experimenting without looking for suitable packages
• Enable recommending practices to tier packages

[sabine]

Reopening because having ocaml.org be tested as a reverse dependency on opam-repository CI is useful.