allow using "exists" with direct attributes

[Roguelazer]

Allows you to do a query like

clusto-query public_ip exists

to show all items with a public IP

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}