(feat) add support for musl using cross-rs

[jprendes]

This PR adds support for building and testing against musl targets.

A summary of changes:

• Add musl targets to Cross.toml and the corresponding Dockerfile.musl
• Install dependencies in Dockerfile.gnu so that we can run tests using cross.
• Add a cargo.sh script that wraps cargo calls, using either cargo or cross based on the target.
• Fix mock.rs so that it builds with musl targets
• Use the cargo.sh script in the features_test.sh and justfile
• Remove now redundant musl_test.sh.
• Update CI to install cross, use cargo.sh, and force using cross for all targets (including host target).
• Update CI to relese musl binaries as well as gnu binaries.

Example of a release generated from this PR: https://github.com/jprendes/youki/releases/tag/v0.4.1

Note: This PR builds on top of #2541. I will rebase once that is merged.

[codecov-commenter]

Codecov Report

Merging #2536 (06d8e9f) into main (e3cafbd) will increase coverage by 0.02%.
Report is 5 commits behind head on main.
The diff coverage is 77.77%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2536      +/-   ##
==========================================
+ Coverage   65.86%   65.88%   +0.02%     
==========================================
  Files         133      133              
  Lines       16795    16819      +24     
==========================================
+ Hits        11062    11082      +20     
- Misses       5733     5737       +4     

[utam0k]

Sorry, I won't be able to find the time this week, so I'll look at it in a few days 🙏

[jprendes]

Reabsed.
@utam0k @adrianalin @cuisongliu PTAL

An example release generated by this PR is:
https://github.com/jprendes/youki/releases/tag/v0.3.2

[YJDoc2]

Self-reminder : need to update merge CI requirements to correct CI names after this is merged.
(The three pending CI seems to be because of renaming of the workflows, so should be ok.)

[utam0k]

May I ask a favor of the documentation for developers in another PR?
https://containers.github.io/youki/developer/introduction.html

[utam0k]

Thanks!! @jprendes

[utam0k]

Self-reminder : need to update merge CI requirements to correct CI names after this is merged. (The three pending CI seems to be because of renaming of the workflows, so should be ok.)

Done ✅

[YJDoc2]

Thanks @utam0k 💜
Is this ready to merge? The CI checks which are updated in this are keeping other PRs from passing...
I can revert the CI check requirements temp until this is merged, or as we don't have anything urgent, just wait out for this.
Let me know.

[YJDoc2]

LGTM 👍

I have some nitpicks / questions, but nothing that would block merging, so as @utam0k has already approved, I'll wait sometime and merge this.

@jprendes thanks a lot for this, this is really amazing work! Take your time for replying to the comments 👍

[utam0k]

Ops sorry I'll merge it

[adrianalin]

Sorry, I could not find where documentation was updated (related to musl build), @jprendes please provide link. Thank you!

[jprendes]

Sorry, I could not find where documentation was updated (related to musl build)

I still need to create a PR. I'll do that as soon as I have some bandwidth again.