Make system state *.toml files writing more robust

[m-blaha]

If dnf5 runs out of disk space during a transaction, it is currently possible that the data written to the /usr/lib/sysimage/libdnf5/*.toml files are incomplete. To prevent this, we should consider writing the files to a temporary location first, and then move the complete files to the final destination.

See #1550 for more context.