opam: add without-ocaml option.
opam: add without-ocaml option.

The without-ocaml option enables to install opam without the
installation of ocaml and camlp4.

Closes #48574.

Signed-off-by: Mike McQuaid <a17fed27eaa842282862ff7c1b9c8395a26ac320@mikemcquaid.com>

filcab/homebrew,filcab/homebrew,filcab/homebrew,filcab/homebrew