Make pg_createsubscriber more wary about quoting connection parameters.
The original coding here could fail with database names, user names,
etc that contain spaces or other special characters.
As partial test coverage, extend the 040_pg_createsubscriber.pl
test script so that it uses a generated database name containing
funny characters.
Hayato Kuroda (some mods by me), per complaint from Noah Misch
Discussion: https://postgr.es/m/
20240623062157.97.nmisch@google.com