Make borgbackup read-only

[szaimen]

Address part of #2506

• needs allow to add tmpfs #2811

[Zoey2936]

you could also add VOLUME /tmp to the dockerfile

[szaimen]

you could also add VOLUME /tmp to the dockerfile

I tried this. Unfortunately it does not play well when converting to kubernetes. So better to use tmpfs for that because it works out-of-the-box and is intended for that purpose IIRC :)