Cookbook recipes to parse command-line arguments

[boechat107]

The recipes in this PR contains three alternative ways to parse command-line arguments:

1. Manipulating Sys.argv directly.
2. Using the Arg module from the standard library.
3. Using Cmdliner installed through opam.

[boechat107]

I can't understand why the CI failed. I'll investigate ood-gen.

If someone has seeing this before, I would appreciate any help.

[cuihtlauac]

This needs to be rebased against a fresh main

[cuihtlauac]

See also #2573

[sabine]

Closing because https://github.com/ocaml/ocaml.org/pull/2573 was merged.