Add build files for ARM

[scottyeager]

This PR adds Dockerfiles and Github workflows to automatically build containers for the ARM architecture upon new releases (see #11).

A few notes:

• All changes are adjacent to the existing workflows, to prevent any issues or complications with the mainline builds
• The container images are tagged with a suffix -arm, for example latest-arm or 0.2.0-arm. While different architecture can coexist under a single tag, it's only possible if all are built under a single workflow run (avoided to preserve the point above)
• Since this and the other workflows needed to support the full farmerbot deployment only trigger when a new tag/release is issued, I've waited to include the new docker-compose.yaml file until all are ready. For now, that file is available on my fork and points to the containers built on the set of forks I used for testing
• Any suggestions regarding how to organize the new files, in terms of directory structure or naming conventions, are welcome

[brandonpille]

Alright thanks for the changes. I guess we can merge?