order and setup new backup server (backup-storage-01)

The new backup server (#41364 (closed)) has been approved.

@lavamind can you settle the specs, and order the box? i'm happy to review and approve the hardware if you don't feel fully confident, of course...

i also put the server setup in this issue, but we can also spin that out in a separate one if we want to... one thing that's for sure is we want to move to barman for the psql backups (#40950), but one ... uh... problem with that approach is that we actually want cross-backups, so, technically, we can't actually deploy that on the new server ... oops?

so maybe we need to move other psql databases and we'll have to resize the partition anyways? urghl.

thanks!