Handle logical slot conflicts on standby

Handle logical slot conflicts on standby

During WAL replay on the standby, when a conflict with a logical slot is
identified, invalidate such slots. There are two sources of conflicts:
1) Using the information added in 6af1793954e, logical slots are invalidated if
   required rows are removed
2) wal_level on the primary server is reduced to below logical

Uses the infrastructure introduced in the prior commit. FIXME: add commit
reference.

Change InvalidatePossiblyObsoleteSlot() to use a recovery conflict to
interrupt use of a slot, if called in the startup process. The new recovery
conflict is added to pg_stat_database_conflicts, as confl_active_logicalslot.

See 6af1793954e for an overall design of logical decoding on a standby.

Bumps catversion for the addition of the pg_stat_database_conflicts column.
Bumps PGSTAT_FILE_FORMAT_ID for the same reason.

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: Alvaro Herrera 
Discussion: https://postgr.es/m/20230407075009[email protected]