add to releases Concourse worker for darwin arm64 architecture (Apple M1)

[marco-m-pix4d]

Hello,

we run in production a Concourse worker for darwin arm64 on Apple M1; it works fine :-)
We kindly ask to consider adding to the releases a binary for this architecture.

thanks!

There is a similar discussion about Linux arm64 in #1379, but this ticket instead is about darwin arm64 and worker only.

[Esysc]

It'd be good also have the fly client included in the assets for Apple M1.

[siennathesane]

I would also like a fly client included in the assets for the Apple M1 so I can download it from the UI

[aliculPix4D]

Update: cloudfoundry/garden-runc-release#233 (comment)