Update docs of logical replication for commit 8d74fc9.

After commit 8d74fc9, the details of logical replication conflicts can
be found in pg_stat_subscription_workers view.

Author: Masahiko Sawada
Reviewed-by: Amit Kapila
Discussion: https://postgr.es/m/CAD21AoC+zm5tGN8x88AJZYcX0g_eiEuu5XdrksNmSeR3Xzwjfg@mail.gmail.com

Author: Amit Kapila

doc/src/sgml/logical-replication.sgml

@@ -346,7 +346,9 @@
   <para>
    A conflict will produce an error and will stop the replication; it must be
    resolved manually by the user.  Details about the conflict can be found in
-   the subscriber's server log.
+   <link linkend="monitoring-pg-stat-subscription-workers">
+   <structname>pg_stat_subscription_workers</structname></link> and the
+   subscriber's server log.
   </para>
 
   <para>