Insurance — Uninsured motorist — Passenger in rental car who was injured in an accident involving an uninsured/underinsured motor vehicle was not an “insured person” entitled to UM coverage under driver’s insurance policy where rental car did not meet policy’s definition of “covered auto” — Rental car was not a permanent replacement for vehicle insured under driver’s policy, and insured driver was not a beneficial owner of the rental vehicle such that rental vehicle fit into policy’s definition of an “additional auto”