fix: enable docker buildkit

[jeqo]

Solves this kind of issues:

Step 7/22 : COPY --from=scratch /code/ .
invalid from flag value scratch: image with reference 
sha256:b12ae8e35357a7aa30ed72e5e406a61e1c287ba96471601b43c8e066f6795fa6 was found but does not match the 
specified platform: wanted linux/arm64, actual: linux/amd64

Test it with:

build-bin/docker/docker_build openzipkin/zipkin-aws:test

[jcchavezs]

Yay!