Skaffold: (Feature request) Support docker buildx build

[hach-que]

We're currently using skaffold with buildkit enabled. We found a bug in buildkit (https://github.com/moby/buildkit/issues/1072#issuecomment-511468942) and they've since fixed it, but now we need to use the new version of buildkit in our infrastructure.

The recommended way of using a newer version of buildkit than the one DOCKER_BUILDKIT=1 provides is docker buildx: https://github.com/docker/buildx

We use skaffold for our builds, so in order to use buildx, we need skaffold to be able to use it as an alternative to docker build.

[hach-que]

Closing this for now as apparently you can use newer versions of Buildkit by just using the # syntax feature: https://github.com/moby/buildkit/issues/1072#issuecomment-511487993

[AndiDog]

@balopat @nkubala Mind reopening this? I see huge benefits from support buildx and its --cache-to feature: as opposed to plain DOCKER_BUILDKIT=1 execution, buildx can upload the cache for all parts of a multi-stage build and would therefore save lots of time (and the environment).

[no1melman]

This would be great to re-open for that exact issue above - we've tested using docker buildx build using the caching and it works a treat, it would shave literally hours off of our builds and would be a massive boon to our work

[briandealwis]

So you can configure Docker so that docker build uses buildx by default with docker buildx install. If you combine that with useDockerCLI: true then you'll be using buildx.

Adding support for --cache-to is a bit more difficult. Docker labels buildx as an experimental feature that may change without notice. So I'm a bit leery about adding adding dedicated fields for builder options that may be changed, renamed, or removed without notice. Perhaps we should incorporate the Kaniko builder's now-removed AdditionalFlags.

[no1melman]

I think any way we can add extensibility to the API so we can leverage these features would be great. AdditionalFlags sounds great, I understand not creating specialised fields.