Adding flag to sort incident list by field name (with reverse option and multiple fields support)

[mbovo]

As per title, this would work like:

pdh inc ls --sort assignee --reverse

In case the field is not found the cli will notice you and print the list of available fields

 pdh inc ls -e --sort unkn --reverse                                
Invalid sort field: unkn
Available fields: id, assignee, title, status, created_at, last_status_change_at, url