Add Docker's "buildkit" CLI to "arkade get"

[alexellis]

The buildkit (client) and buildkitd (builder daemon) can both be used with faasd or k3s hosts for building images without installing Docker onto the machine.

There is a tar that can be downloaded like we do with inletsctl, however, we need to make sure we extract both binaries. I'm fairly sure that this will "just work"

See more:

https://github.com/moby/buildkit/releases

[alexellis]

@yankeexe would you like to take this and/or #242 ?

[yankeexe]

I can take this one @alexellis

[alexellis]

Great, thank you :+1: It may be quicker if you also take #242 at the same time - they are similar tools and touch the same files.

[alexellis]

This is up for grabs after having been left in flux for a year today.

I needed buildkit today and it would have been great if this had been completed.

[alexellis]

Edit these files:

First add tests matching the releases on the download page for Buildkit:

https://github.com/alexellis/arkade/blob/master/pkg/get/get_test.go

Then add a Go template here, and test it with "go build ./arkade get buildkit" and with the unit tests "go test -v ./..."

https://github.com/alexellis/arkade/blob/master/pkg/get/get.go

[alexellis]

/add label: help wanted, good first issue

[leninkumar31]

I am gonna take this one @alexellis

[alexellis]

Thanks. When do you think you'll have something up in a pull request?

[leninkumar31]

I am working on it now. I will try to raise PR by end of today.

[alexellis]

@NikhilSharmaWe we didn't get this added in the end, could you send a PR for it?

This is different from a system app, so have a look at a few merged PRs to see what kind of testing we look for etc.