[Feature] Allow user to reorder column view

[C0rn3j]

I was sort of hoping setting -output would reorder the columns by its content on its own.

  -output string
        output fields: mountpoint, size, used, avail, usage, inodes, inodes_used, inodes_avail, inodes_usage, type, filesystem

However
duf -output 'mountpoint, usage, filesystem' (default sort) and
duf -output 'filesystem, mountpoint, usage' are functionally identical.

I would welcome if my ordering in the output was respected.
To not break things for users as is, maybe it should be hidden behind a -order-columns: default, custom flag.