Support M1 (arm64) Macs

[yarikoptic]

• original issue came up in
• troubleshooted to needing to use -arm64 based images from https://quay.io/repository/singularity/singularity?tab=tags

so we need to

• establish building both amd64 and arm64 docker images (now only amd64 and likely not automated)
• adjust singularity_cmd to switch to -arm64 whenever uname -m says arm64.

NB I was wondering if we could move provisioning of image we do in https://github.com/ReproNim/containers/blob/master/scripts/Dockerfile.singularity-shim to somehow to be done at initial run-time -- then we could avoid needing to build our image at all. But it would also make it less trivial to update and harder to troubleshoot. so let's stay with built images but may be move over to quay.io for them

[yarikoptic]

current show stopper is seems that quay does not provide option for the builders to be of another architecture, so the build of -arm64 flavor fails. May be we are doomed to automate builds on github actions instead of relying on quay, as @vsoch did in http://github.com/singularityhub/singularity-docker//blob/HEAD/.github/workflows/build-containers.yaml

[vsoch]

@yarikoptic we don't build in quay, we just push there.

[vsoch]

oh right you noted that, and this is a totally different issue! lol wonk wonk someone needs to put on her glasses... squintysarus