Issue: Feature Request

Is your feature request related to a problem? Please describe.
There doesn't currently seem to be a way of importing environment variables into gunicorn and workers using the supervisor environment= feature. This would be useful for dependencies that look at os.environ, etc

Describe the solution you'd like
Modify bench setup supervisor to import this config from site_config.json, maybe a key called environment

Describe alternatives you've considered
There doesn't appear to be any other way of passing environment variables to gunicorn
I looked at dotenv but seems overkill to include another dependency

Additional context
https://stackoverflow.com/questions/12900402/supervisor-and-environment-variables