Use Docker secrets (#340)

docker/entrypoint.sh

@@ -9,4 +9,10 @@ usermod -o -u "$UID" $USER
 chown -R "$USER:$USER" /opengist
 chown -R "$USER:$USER" /config.yml
 
+if [ -f "/run/secrets/opengist_secrets" ]; then
+    set -a
+    . /run/secrets/opengist_secrets
+    set +a
+fi
+
 exec su $USER -c "OG_OPENGIST_HOME=/opengist /app/opengist/opengist --config /config.yml"