PQL: Design a methodology for descending into hashes for facts and such

Right now searching across structured facts with PDB involved matching the name and value, we should devise a way in PQL to do a search using leaf and value instead, sort of like this.

networking.eth0.macaddress ~ '^aa:00:bb'

This might involve some backend AST work to be done to support this also.

This ticket is the design work, to decide exactly how the syntax would look like, then determine the work and tickets involved to implement it.

If we can, I'd like to see us also use this same methodology for drilling into other hashes, such as resource parameters and such.