Run nginx and gunicorn in docker via supervisor

[c-w]

Currently the nginx process is run in the background of the docker container and the gunicorn process is run in the foreground. This means that if the nginx process crashes, it won't get restarted and the nginx
logs don't show up in the docker logs since only the foreground gunicorn logs are captured. More generally, it is also not recommended to run multiple processes in a single docker container unless a process manager is used (more information).

This change introduces the supervisor process manager to run as the single foreground process in docker. The supervisor process in turn takes care of running both nginx and gunicorn.

Note that supervisor has its own environment variable isolation and doesn't have an easy way of passing all the environment variables to the child process. As a work-around to avoid having to declare all environment variables multiple times, we first dump the environment into files and then reload them in the child process from the files via the envdir utility.

Also:

• Always dereference envs via os.getenv to make it easier to find all the environment variables used in the project via grep.
• Modify the gunicorn custom logger to fix line length and unused import warnings and fix runtime crash when not in GCP or Azure.
• Fix startup crash in docker-compose due to missing bash executable.

[colinschoen]

LGTM

Excellent