Produce arm64 snaps

[Imberflur]

I tried to figure this out as part of reviving the snap, however there were a few barriers which made this difficult.

1. Gtihub action runners are only x86_64 (no aarch64 machines).
2. Cross-compiling with snapcraft is not very straightforward or well supported. Most discussion on this points to snapcraft's build services that offer arm machines however these services have caveats that make them less than ideal.
3. I don't actually have any device to test the result with!

Here are the options I was able to research for potential methods to get arm64 builds working each of which has various caveats. Note, the premise is that we want to be able to automate when builds are produced in order to deliver security updates (that is updates of the dependencies built into the packaged snap) (and as a bonus this makes creating new releases easier).

• Use the "build from github" service offered by snapcraft https://snapcraft.io/docs/build-from-github
  • No auto builds when security updates are needed (maybe we could setup something were a github action pushes to a branch when a new build is needed for security updates).
  • I'm not sure how much control is given for selecting what branch is published to.
• Use the "remote build" service https://snapcraft.io/docs/remote-build
  • Not designed to be used in CI https://forum.snapcraft.io/t/automate-snapcraft-remote-build-on-github-actions/24447/2
• Use a free CircleCI account (they offer arm runners) https://snapcraft.io/tutorials/continuous-snap-delivery-from-circle-ci#1-overview
  • Would need to create an account with this service and learn how to use it.
• Figure out cross-compiling with snapcraft https://forum.snapcraft.io/t/state-of-cross-compiling-a-non-trivial-snap-amd64-to-armhf/20888