pgstat: add pg_stat_have_stats() test helper.
Will be used by tests committed subsequently.
Bumps catversion (this time for real, the one in
0f96965c658 got lost when
rebasing over
5c279a6d350).
Author: Melanie Plageman <melanieplageman@gmail.com>
Discussion: https://postgr.es/m/CAAKRu_aNxL1WegCa45r=VAViCLnpOU7uNC7bTtGw+=QAPyYivw@mail.gmail.com