darwin arm64 binaries not provided for secondary binaries

[mikn]

Whilst there is a darwin arm64 binary for the main cfssl binary, you do not currently build any for secondary binaries, such as cfssljson or multirootca. This would be very helpful.

As a secondary request, it would also be very useful if you provided some kind of checksum file, either per binary or one per artefact release.

[arulrajnet]

This will be useful for who runs cfssl on latest MacOS.

We have to add arm64 in

• https://github.com/cloudflare/cfssl/blob/master/.goreleaser.yml#L202
• https://github.com/cloudflare/cfssl/blob/master/.goreleaser.yml#L276

Will give PR.