fix: ignore mkdir if folders exist

Dockerfile

@@ -38,7 +38,7 @@ RUN CGO_ENABLED=0 go build \
     -ldflags='-w -s -extldflags "-static"' -a \
     -o /app/backoffice-server .
 
-RUN mkdir /app/mnt /app/mnt/configs
+RUN mkdir -p /app/mnt /app/mnt/configs
 
 RUN chown -Rf "${UID}" ./*