Doc: Fix the wrong link on pg_createsubscriber page.
Commit
84db9a0eb1 has added the incorrect link to
'initial data synchronization'. It was a subsection of Row Filter and
didn't provide the required information.
Author: Peter Smith
Reviewed-by: Vignesh C, Pavel Luzanov
Backpatch-through: 17, where it was introduced
Discussion: https://postgr.es/m/CAHut+PtnA4DB_pcv4TDr4NjUSM1=P2N_cuZx5DX09k7LVmaqUA@mail.gmail.com