Switch to single-process (uvicorn) container

[danielballan]

Closes #282

• Remove gunicorn from the containerized deployment
• Turns Prometheus metrics on by default
• Makes the multiprocess mechanism in Prometheus (the memory-mapped files) optional, off by default
• Simplifies Dockerfile
• Moves the code that checks for scalable config settings out of a one-off script and into the CLI as --scalable

[dylanmcreynolds]

I think this is a great simplification. Gunicorn was seen as a necessary step to acheive scaling, but the realization that even docker-compose can easily perform round-robin load balancing lets us take a lot of complexity out of containers and into the deployment, where it belongs.

It is truly sad that podman-compose doe not achieve this out of the box. In that case, one could imagine a gunicorn container and multiple tiled containers to achieve horizontal scaling.