Apple Silicon ARM64 Support/Go Modernisation

[DomT4]

I suspect this is going to be deemed overambitious/overkill but perhaps it'll be a good launching pad for discussion. Currently this project does not support the new Apple Silicon, because there's no darwin/arm64 binary available; this PR fixes that by folding in everything necessary to create one going forwards.

Due to Go only very recently adding support for darwin/arm64 this has resulted in a significant minimum Go version bump, which led me to take advantage of the other features that could then be relied upon as available such as using go mod instead of having to use an external dependency manager. This PR also bumps the version, primarily because Build.sh seems designed to not rebuild existing versions?

I don't use this project locally, so I would recommend testing it a bit if you are interested in using this PR. My motivation was Homebrew's formula test failing for akamai/cli because of purge not having a platform-suitable binary available. This should also address https://github.com/akamai/cli-purge/issues/21.

[DomT4]

~> file cli-purge/build/akamai-purge-1.0.2-macarm64
cli-purge/build/akamai-purge-1.0.2-macarm64: Mach-O 64-bit executable arm64

~>  cli-purge/build/akamai-purge-1.0.2-macarm64 --version
akamai-purge version 1.0.2

[lkowalsk-akamai-com]

Thank you for your contribution, but we handled this work separatelly.