USER instruction enabled in Dockerfile

- avoid running gunicorn as root user
- use setcap to allow gunicorn starting with a privileged port
- write permission only on /app/configs folder
- su command removed from entrypoint.sh, because it runs as pda user

docker/entrypoint.sh

@@ -7,13 +7,9 @@ GUNICORN_WORKERS="${GUNICORN_WORKERS:-4}"
 GUNICORN_LOGLEVEL="${GUNICORN_LOGLEVEL:-info}"
 BIND_ADDRESS="${BIND_ADDRESS:-0.0.0.0:80}"
 
-cat ./powerdnsadmin/default_config.py ./configs/docker_config.py > ./powerdnsadmin/docker_config.py
-
 GUNICORN_ARGS="-t ${GUNICORN_TIMEOUT} --workers ${GUNICORN_WORKERS} --bind ${BIND_ADDRESS} --log-level ${GUNICORN_LOGLEVEL}"
 if [ "$1" == gunicorn ]; then
-    # run as user pda so that if a SQLite database is generated it is writeable
-    # by that user
-    su pda -s /bin/sh -c "flask db upgrade"
+    /bin/sh -c "flask db upgrade"
     exec "$@" $GUNICORN_ARGS
 
 else