Show all disks in disk widget, not just those currently mounted

[pwige]

Checklist

• I've looked through the documentation and existing open issues for similar feature requests.

Describe the feature request

It would be nice if the disk widget showed all disks on the system, not just those currently mounted. Currently, if I'm writing straight to a block device (e.g., /dev/sda with dd) and that device isn't mounted, it is completely excluded from the disk widget's output.

While it doesn't show individual disks, htop does show overall disk-usage, even for unmounted block devices.

It is annoying having to switch from btm to htop to get this information when the disk widget is already showing *some* disk-usage information.

[ClementTsang]

Hmmmm I'll need to see if that's doable. Seems reasonable though.

[pwige]

Much appreciated!