Allow $REDASH_WEB_WORKERS to be set in the environment to change the
number of Gunicorn workers that are started (currently hardcoded to
four). If not set, the default is four, so this will not affect
existing users at all.
Documentated by example in docker-compose example manifests.
1. Simplify user creation to create a non system user (so the uid will usually
match the host user).
2. Set the user to redash & remove the need to change user in docker entrypoint.
