Support Darwin arm64 builds

[pmalek]

Given that kdigger is written in Go it should be fairly straightforward to provide those builds.

[mtardy]

Sorry for the late reply but yes it should be fairly straightforward, feel free to update the Makefile release target in a PR to add darwin_arm64 and change darwin into darwin_amd64. It will be my pleasure to merge this and then do the release on the GitHub repo.