Support for download of ARM binaries for Macs

[gwidion]

Downloading helm client on Mac will always download amd64 binaries.

    fun getOperatingSystemClassifier() =
        when {
            osName.startsWith("Mac OS X") ->
                "darwin-amd64"

I think this should easily allow downloading arm64 binaries when appropriate.

fun getOperatingSystemClassifier() = 
    when {
        osName.startsWith("Mac OS X") -> 
            when (osArch) {
                "aarch64" -> "darwin-arm64"
                else -> "darwin-amd64"
            }

[gwidion]

any progress? should I open a MR?

[JamieSlome]

@gwidion - if you have changes you'd like to suggest, please feel free to open a pull request! 👍