Currently tab completion for ALTER DATABASE RESET shows a list of all
configuration parameters that may be set on a database, irrespectively
of which parameters are actually set. This patch improves tab completion
to offer only parameters that are set.
Author: Robins Tharakan Reviewed-By: Tomas Vondra
Discussion: https://postgr.es/m/CAEP4nAzqiT6VbVC5r3nq5byLTnPzjniVGzEMpYcnAHQyNzEuaw%40mail.gmail.com