Logical replication

- Add PUBLICATION catalogs and DDL
- Add SUBSCRIPTION catalog and DDL
- Define logical replication protocol and output plugin
- Add logical replication workers

From: Petr Jelinek <petr@2ndquadrant.com>
Reviewed-by: Steve Singer <steve@ssinger.info>
Reviewed-by: Andres Freund <andres@anarazel.de>
Reviewed-by: Erik Rijkers <er@xs4all.nl>
Reviewed-by: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>

src/backend/executor/execMain.c

@@ -43,6 +43,7 @@
 #include "access/xact.h"
 #include "catalog/namespace.h"
 #include "catalog/partition.h"
+#include "catalog/pg_publication.h"
 #include "commands/matview.h"
 #include "commands/trigger.h"
 #include "executor/execdebug.h"
@@ -1024,7 +1025,7 @@ CheckValidResultRel(Relation resultRel, CmdType operation)
 	{
 		case RELKIND_RELATION:
 		case RELKIND_PARTITIONED_TABLE:
-			/* OK */
+			CheckCmdReplicaIdentity(resultRel, operation);
 			break;
 		case RELKIND_SEQUENCE:
 			ereport(ERROR,