Check the remaining space before creating the backup

Issue #19 (closed)

This MR here works on top of https://gitlab.hzdr.de/hub-terra/sms/orchestration/-/merge_requests/25 and adds checks for remaining space on the target folders (local & on the project share).

While the checks for the project share are quite easy (because we know how large the files are that we want to copy over there), the check for the vm itself is a bit harder.

I currently set a hard limit that we need to have one GB left (for both stagung & prod).

With the currently available space (asuming 1 backup per day) we will run earlier into trouble storing the backup on the project share (180 backups on 20 GB) then on our local machine (30 backups on 9.3 GB).