The old KSysGuard (plasma/ksysguard>) can monitor the whole disk activity. The current disk plugin can only monitor partitions. This MR changes disk plugin for showing hard drives too (nvme0n1, sda, sdb...).
Now disk plugins search for StorageVolume instead StorageAccess. Obvious it can not monitor free space on non partition volume so that is skiped.
This MR needs a code review. For example, I do not know if nested ternary is allowed. I also do not know if I write a good explanation on commit message (English is not my native language).