Add `disk_use_binary_prefix` config option

[ev-dev]

Checklist

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

Describe the feature request

The current disk widget defaults to showing sizes in decimal/SI units (MB,GB,TB...) and should be configurable with an option and CLI flag, similar to the existing network_use_binary_prefix implementation.

This would make bottom more cross-platform friendly since many tools on Windows default to showing disk sizes in binary prefixes (KiB, MiB, GiB...) which differ from the values shown in bottom, especially for larger volumes.

[ClementTsang]

Can take a look at this.