doc: Clarify some terms for pg_createsubscriber

doc: Clarify some terms for pg_createsubscriber

The last section of pg_createsubscriber used the terms
"publication-name", "replication-slot-name", and "subscription-name".
These terms are not defined on the page, which was confusing, and the
intention is clearly to refer to the values one would give to the
options --publication, --subscription and --replication-slot.  Let's
simplify the documentation by mentioning the option switches, instead of
these terms.

Reported-by: Christophe Courtois
Author: Shubham Khanna
Reviewed-by: Vignesh C, Peter Smith
Discussion: https://postgr.es/m/173288198026.714.15127074046508836738@wrigleys.postgresql.org
Backpatch-through: 17