Create docker image for arm64

[pedroapfilho]

I was installing zombienet from docker hub to run it, but then I saw that it doesn't have support for arm64, making it very tricky to run.

This could be mitigated by having support for arm64, and adding documentation for how to run it properly.

[pedroapfilho]

Context, when I fetch the image from the hub: https://hub.docker.com/r/paritytech/zombienet and try to run it using:

docker run paritytech/zombienet:latest

it gives me:

WARNING: The requested image's platform (linux/amd64) does not match the detected host platform (linux/arm64/v8) and no specific platform was requested

[wirednkod]

Thank you @pedroapfilho

We have a relative issue about this so I will close this as duplicate. You can follow the discussion on the other issue: #710