Add feature ocaml-opam

[mrBen]

I know that ocaml-asdf and opam-asdf already exist, but:

• I don't want to use OCaml without opam
• opam-asdf only installs opam, then I have to initialize it, then install OCaml
• they don't include convenient things like the build system, an LSP, the VS Code extension, etc.
• I don't know what asdf is, so I don't really want to use it 😅

Both seem auto-generated, with no real intention of providing a usable development environment out of the box.

I started from scratch, following the installation process given on the OCaml site.

---

I still have a few details to work out:

• gh-release doesn't download the latest version of opam
• platform tools are systematically installed; this should be disableable
• if the project uses opam as a dependency manager (which is likely), have an option to pre-install the project's dependencies

I don't know if I should publish it and improve it later, or keep it as a draft until I've solved these details?

[koralowiec]

Heyo!

I don't know if I should publish it and improve it later, or keep it as a draft until I've solved these details?

I think it should be fine to release the feature with the current scope (so you can mark it as ready for review).

You can create separate issues for the todos which you listed, and I'll assign you to them.

gh-release doesn't download the latest version of opam

This one seems strange, so I may lend a hand (maybe something is wrong with gh-release feature)

[mrBen]

I'll create the issues.

For gh-release, instead of getting opam 2.3.0, it gets 2.3.0~rc1, which is the latest pre-release. I wanted to look a bit further to open a proper issue, but I haven't had the time yet.

[koralowiec]

Oh, this one is a know issue on nanolayer side (devcontainers-extra/nanolayer#1). I have to finally fix it...

As a workaround you can use regex for releases (like I did for helmfile feature):

--option releaseTagRegex='^(?!.*(alpha|beta|rc)).*$'

This should filter out the releases that contain alpha, beta, or rc in their names

[koralowiec]

Looks fine, I only have a small change request

[koralowiec]

The feature will be available after this job is run

[koralowiec]

Feature is available: https://github.com/devcontainers-extra/features/pkgs/container/features%2Focaml-opam