Load env file in config/.env automatically to avoid sourcing it by hand (#626)

Automatically load .env file
^^^^^^^^^^^^^^^^^^^^^^^^^^^^

On non-docker deployments, earlier versions required you to source
the config/.env file before launching any Funkwhale command, with ``export $(cat config/.env | grep -v ^# | xargs)``
This led to more complex and error prode deployment / setup.

This is not the case anymore, and Funkwhale will automatically load this file if it's available.