This enables running PG's standard testsuite with a PG server configured
for decoderbufs.
Example on Debian:
```
$ sudo apt install postgresql-14-decoderbufs
$ pg_virtualenv -o shared_preload_libraries=decoderbufs -o wal_level=logical
Creating new PostgreSQL cluster 14/regress ...
$ make installcheck
/usr/lib/postgresql/14/lib/pgxs/src/makefiles/../../src/test/regress/pg_regress --inputdir=./ --bindir='/usr/lib/postgresql/14/bin' --dbname=contrib_regression decoderbufs
(using postmaster on localhost, port 5433)
============== dropping database "contrib_regression" ==============
HINWEIS: Datenbank »contrib_regression« existiert nicht, wird übersprungen
DROP DATABASE
============== creating database "contrib_regression" ==============
CREATE DATABASE
ALTER DATABASE
============== running regression test queries ==============
test decoderbufs ... ok 30 ms
=====================
All 1 tests passed.
=====================
$ exit
Dropping cluster 14/regress ...
```
Christoph Berg
Jiri Pechanec
Garrett T
Danila Kiver
Xavier Stevens