Convert additional build context paths on Windows

[l0rd]

This PR partially fixes issues with the option --build-context <label>=<path> of podman build.

This is enough to fix #17313 on macOS and Windows WSL with the default machine mounts.

A complete fix of the option --build-context would require packaging the additional build contexts in some additional tars and update the /libpod/build endpoint to accept multi-part HTTP requests. But that's outside the scope of this PR.

Does this PR introduce a user-facing change?

Fix VisualStudio Dev Containers Features on Windows

[rhatdan]

LGTM
@n1hility @baude @ashley-cui PTAL

[mheon]

Is this something we can test?

[l0rd]

Is this something we can test?

I am going to add an e2e test. Converted it back to draft mode.

[n1hility]

LGTM

[l0rd]

I have added a new e2e machine test podman build contexts in pkg/machine/e2e/basic_tests.go.

I have also updated pkg/machine/e2e/README.md with more instructions to run the tests on windows. There are also a couple of small fixes in build_windows.md that are unrelated to the additional contexts but too small to deserve a dedicated PR.

Tests are green. I am switching this PR back to ready for review.

[l0rd]

@containers/podman-maintainers PTAL

[rhatdan]

/approve
/lgtm

[openshift-ci]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: l0rd, rhatdan

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[worldofgeese]

Does this mean Podman will now just work with Dev Containers? I can scarcely contain my excitement!

[l0rd]

Does this mean Podman will now just work with Dev Containers? I can scarcely contain my excitement!

A few clarifications:

• This is now merged in main branch and will be included in next stable version of Podman (i.e. v5.3.0)
• The machine provider needs to be WSL (Hyper-V supports needs Error running podman build with option --build-context on Hyper-V #23429)
• The devcontainer.json should include the following runArgs and containerEnv (but I think it may be avoided in rootless mode):

    "runArgs": [
    "--userns=keep-id"
    ],
    "containerEnv": {
    "HOME": "/home/node"
    }

[JustinGrote]

@l0rd thank you!