Add some basic tests for progress reporting of COPY

Add some basic tests for progress reporting of COPY

This tests some basic features for progress reporting of COPY, relying
on an INSERT trigger that gets fired when doing COPY FROM with a file or
stdin, checking for sizes, number of tuples processed, and number of
tuples excluded by a WHERE clause.

Author: Josef Šimánek, Matthias van de Meent
Reviewed-by: Michael Paquier, Justin Pryzby, Bharath Rupireddy, Tomas
Vondra
Discussion: https://postgr.es/m/CAEze2WiOcgdH4aQA8NtZq-4dgvnJzp8PohdeKchPkhMY-jWZXA@mail.gmail.com