Publishing multi-arch images depends on Docker Desktop

[tmds]

I'm trying to publish this app with /t:PublishContainer on Fedora 42:

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net10.0</TargetFramework>
    <ImplicitUsings>enable</ImplicitUsings>
    <Nullable>enable</Nullable>
    <RuntimeIdentifiers>linux-x64;linux-arm64</RuntimeIdentifiers>
    <ContainerRuntimeIdentifiers>linux-x64;linux-arm64</ContainerRuntimeIdentifiers>
  </PropertyGroup>

</Project>

The publish fails with:

    [Microsoft.NET.Build.Containers.Tasks.CreateImageIndex] Building image index 'console:latest' on top of manifests sha256:f587de8b2272fd9ccd7b0545dea6d14b5f3c2159f031e878753142aa18f86ace, sha256:18375ce87fe86458e1245df28691ac25ecbc23c85fc346f433610a0c58e48b6b.
    /usr/lib64/dotnet/sdk/10.0.101/Containers/build/Microsoft.NET.Build.Containers.targets(366,5): error CONTAINER1020: Failed to load image because containerd image store is not enabled for Docker. Tip: You can enable it by checking 'Use containerd for pulling and storing images' in Docker Desktop settings.

I'm on Fedora which ships with Podman instead of Docker.

The dependency on Docker Desktop isn't called out in the documentation. It's not clear if it can work with Podman or how to set that up.

Ideally, this could be made to work without depending on Docker/Podman.

cc @dotnet/sdk-container-builds-maintainers @omajid

[baronfel]

IIRC at the time we implemented this feature Podman did not support load of multi-arch OCI Image Index structures. If this restriction is no longer relevant we can definitely look at enabling this support!

Even if the restriction is in place, we should have a more explicit error that in podman-only scenarios the tooling doesn't support multi-arch publishing.