Make Arquivo run from within Docker

[phillmv]

This PR:

• Adds a Dockerfile template
• Tweaks it, adds final and development stages
• Does a whole bunch of bending over backwards to get ssh to work properly from inside the container's context
• Ditto for fixing weird assumptions the code made, that this was just chillin' on my personal laptop, and instead of a tightly contained (pun intended) environment
• Fixes a bunch of weird bugs that turns out I had on YAML parsing and with serializing attachments to the git repo

After literally 5 months of calendar time and ~1.5 weeks of @phillmv personal time, this sucker will run if you provided it with something like:

docker build --target=development -t arquivo-development:latest .
docker run -it -p 12348:3001 -e -e RAILS_ENV=development -e RAILS_MASTER_KEY=DUMMY -e RAILS_BIND=tcp://0.0.0.0:3001 -v ~/Documents/docker-arquivo/:/data arquivo-development:latest

I can finally switch my locally running copies to using this image! Before I merge this PR I might try to improve the tests, and or get the image to build from within Actions, tho.

[phillmv]

I EVEN FIXED THE CI WORKFLOW :D :D :D

tho I can't get the publishing workflow to work, i think because… it doesn't exist in the default branch yet?

but it's time to try this puppy out and merge and continue to work off the default branch again!