Enhancement: Add --human-readable flag to ls and find commands

Previously, the `ls` and `find` commands showed with the `-l` option 
showed size in bytes, and did not have an option for a more human 
readable format that converted these longer numbers into values such 
as MiB or GiB

The new `--human-readable` option for `ls` and `find` when used with
the `-l` option will convert longer size values into more human friendly
values, with an appropriate suffix depending on the output size. For 
example, a value of `14680064` will be shown as `14.000 MiB`.

https://github.com/restic/restic/issues/4159