Support invalidating replication slots due to horizon and wal_level

Needed for logical decoding on a standby. Slots need to be invalidated because
of the horizon if rows required for logical decoding are removed. If the
primary's wal_level is lowered from 'logical', logical slots on the standby
need to be invalidated.

The new invalidation methods will be used in a subsequent commit.

Logical slots that have been invalidated can be identified via the new
pg_replication_slots.conflicting column.

See 6af1793954 for an overall design of logical decoding on a standby.

Bumps catversion for the addition of the new pg_replication_slots column.

Author: "Drouvot, Bertrand" <bertranddrouvot.pg@gmail.com>
Author: Andres Freund <andres@anarazel.de>
Author: Amit Khandekar <amitdkhan.pg@gmail.com> (in an older version)
Reviewed-by: "Drouvot, Bertrand" <bertranddrouvot.pg@gmail.com>
Reviewed-by: Andres Freund <andres@anarazel.de>
Reviewed-by: Robert Haas <robertmhaas@gmail.com>
Reviewed-by: Fabrízio de Royes Mello <fabriziomello@gmail.com>
Reviewed-by: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>
Reviewed-by: Amit Kapila <amit.kapila16@gmail.com>
Reviewed-by: Melanie Plageman <melanieplageman@gmail.com>
Reviewed-by: Alvaro Herrera <alvherre@alvh.no-ip.org>
Discussion: https://postgr.es/m/20230407075009.igg7be27ha2htkbt@awork3.anarazel.de

doc/src/sgml/system-views.sgml

@@ -2517,6 +2517,16 @@ SELECT * FROM pg_locks pl LEFT JOIN pg_prepared_xacts ppx
        false for physical slots.
       </para></entry>
      </row>
+
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>conflicting</structfield> <type>bool</type>
+      </para>
+      <para>
+       True if this logical slot conflicted with recovery (and so is now
+       invalidated). Always NULL for physical slots.
+      </para></entry>
+     </row>
     </tbody>
    </tgroup>
   </table>