Support invalidating replication slots due to horizon and wal_level

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 6af1793954e 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" 
Author: Andres Freund 
Author: Amit Khandekar  (in an older version)
Reviewed-by: "Drouvot, Bertrand" 
Reviewed-by: Andres Freund 
Reviewed-by: Robert Haas 
Reviewed-by: Fabrízio de Royes Mello 
Reviewed-by: Bharath Rupireddy 
Reviewed-by: Amit Kapila 
Reviewed-by: Melanie Plageman 
Reviewed-by: Alvaro Herrera 
Discussion: https://postgr.es/m/20230407075009[email protected]