[Feature Request]: Add "extension" on "sort-by" configuration

Is your feature request related to a problem? Please describe.
No

Describe the solution you'd like
A way to sort the files by extension like:

~/FolderX/
   > src
    > utils
      utils.h
      view.h
      expr.h
      signal.h
      utils.c
      view.c
      expr.c
      signal.c
    main.c

But only have modification_time and name on the sort_by configuration on nvim-tree.setup {}

Additional context
Nothing

[alex-courtis]

That would be quite useful.