Add builds for ARM64

[justenwalker]

Describe the solution you'd like

I would like for there to be official builds of docker.io/gomods/athens for ARM64
Additionally, it would be nice to have a native build for MacOS M1/M2 chips too

In AWS (and perhaps other cloud providers); ARM CPUs are generally cheaper than Intel/x86_64 ones; however
the docker images and binaries built in this repository are for AMD64 architecture only.

Describe alternatives you've considered

• I could use amd64 CPU instead; but ARM is starting to take over the server market due to its more favorable pricing.
• I could build from source to get arm64 binaries; but then no one else could benefit, unless I were to maintain a fork.

Additional context

goreleaser supports building Universal binaries which packages a single binary for MacOS that supports Intel and Apple Silicon.

[justenwalker]

Looks like #1862 has an implementation

[DrPsychick]

Closing as #1862 has been merged and will be released with 0.13.0

[mloiseleur]

Is there a release planned ?

[DrPsychick]

We're aiming to do a release in the next 2 weeks.