musl detection

[YOU54F]

I'd love to provide musl detection so that we could download a glibc or musl variant of the shared library, depending on the presence of musl as the main libc provider in a particular distro

I had an attempt in the PR

• main...YOU54F:composer-downloads-plugin:main

Which is consumed and tested in a fork on pact-php

Here is a passing run on amd64.

https://github.com/YOU54F/pact-php/actions/runs/8008855755/job/21876520023

arm64 fails due to one of the examples not having a musl variant of roadrunner.

I requested that here

roadrunner-server/roadrunner#1875 (comment)

but I am certain as its built with goreleaser, that it is actually musl based, and we can fall back to it.

That would mean I would need to update my condition to condition the presence of musl, and the architecture (which would be doable)

This initiative to roll out alpine support in PHP is part of

pact-foundation/roadmap#30

Note: plugin/stub server support is not 100% there for musl yet, I need to update out workflows to build musl based static executables, before that is ready to rock.

[tienvx]

I implemented it using your code in 2.1. Thanks for helping me on this