Doc: Move pg_stat_replication_slots view to "Collected Statistics Views" section.

Commit 9868167 added pg_stat_replication_slots view to monitor
ReorderBuffer stats but mistakenly added it under
"Dynamic Statistics Views" section in the docs whereas it belongs to
"Collected Statistics Views" section.

Author: Amit Kapila
Reviewed-by: Masahiko Sawada
Backpatch-through: 14, where it was introduced
Discussion: https://postgr.es/m/CAA4eK1Kb5ur=OC-G4cAsqPOjoVe+S8LNw1WmUY8Owasjk8o5WQ@mail.gmail.com

Author: Amit Kapila

doc/src/sgml/monitoring.sgml

@@ -319,15 +319,6 @@ postgres   27093  0.0  0.0  30096  2752 ?        Ss   11:34   0:00 postgres: ser
       </entry>
      </row>
 
-     <row>
-      <entry><structname>pg_stat_replication_slots</structname><indexterm><primary>pg_stat_replication_slots</primary></indexterm></entry>
-      <entry>One row per replication slot, showing statistics about
-       the replication slot's usage.
-       See <link linkend="monitoring-pg-stat-replication-slots-view">
-       <structname>pg_stat_replication_slots</structname></link> for details.
-      </entry>
-     </row>
-
      <row>
       <entry><structname>pg_stat_wal_receiver</structname><indexterm><primary>pg_stat_wal_receiver</primary></indexterm></entry>
       <entry>Only one row, showing statistics about the WAL receiver from
@@ -627,6 +618,15 @@ postgres   27093  0.0  0.0  30096  2752 ?        Ss   11:34   0:00 postgres: ser
       </entry>
      </row>
 
+     <row>
+      <entry><structname>pg_stat_replication_slots</structname><indexterm><primary>pg_stat_replication_slots</primary></indexterm></entry>
+      <entry>One row per replication slot, showing statistics about the
+       replication slot's usage. See
+       <link linkend="monitoring-pg-stat-replication-slots-view">
+       <structname>pg_stat_replication_slots</structname></link> for details.
+      </entry>
+     </row>
+
     </tbody>
    </tgroup>
   </table>