Allow multiple architectures, image tags for image builds

[Chuxel]

The dev container CLI will soon support a platform argument, and https://github.com/devcontainers/cli/pull/61 introduces the ability to do multiple tags.

The challenge here is when you do a multiple architecture build, you can't use the image to run locally. This makes me wonder if this should either be a separate action, or requires an optional runCmd as proposed with #150.

//cc @stuartleeks

[natescherer]

Just wanted to drop a note that I'm working on a PR to add multiple architecture builds that I expect to wrap up within the next week or so.

[natescherer]

Discovered that this is currently blocked by https://github.com/devcontainers/cli/issues/155

[natescherer]

PR added to allow multi-platform builds. When/if it's accepted I have a plan for how to add multiple tag support, as well.

[joshspicer]

https://github.com/devcontainers/ci/pull/175 has been merged 👍

[natescherer]

Beat me to commenting! I'm now working on adding multiple tag support too.

[metaskills]

Should this be closed now?