Build an image per target os/arch (linux and darwin, amd64 and arm64)

As sylva-toolbox provides binaries to run locally, different docker images are required per target os and arch.

5 tags are created :

• sylva_toolbox:<version> (linux/amd64 for backward compatibility)
• sylva_toolbox:linux-amd64-<version>
• sylva_toolbox:linux-arm64-<version>
• sylva_toolbox:darwin-amd64-<version>
• sylva_toolbox:darwin-arm64-<version>

These images need a linux/amd64 docker daemon to be run.

Depends on sylvactl!183