Support for multi-architecture artifacts

[denisa]

As we started introducing M1 macs, we experienced bad local development experience because our docker images, which contained envoy-preflight/scuttle, were amd64 only.

This PR produces a single docker multi-architecture image, with support for both amd64 and arm64 processors.
At the same time, produces both binaries.

[kvij]

@denisa as you can see in #60 the maintainer lost access and this repo is no longer maintained.
I'm maintaining an up to date fork at https://github.com/kvij/scuttle and currently reworking the github actions (some stuff stops working in may). The plan is to add ARM64 support, Darwin binaries and vulnerability scans.
I'll let you know when I'm done with the rework of the actions and see if that suffices to close this issue.