Add index on pg_publication_rel.prpubid

This should have been added for the benefit of GetPublicationRelations;
let's add it now.

I couldn't measure a performance difference in the TAP tests, but that
may be because the tests use very few publications.

Discussion: https://postgr.es/m/202201120041.p24wvsfcsope@alvherre.pgsql

src/backend/catalog/pg_publication.c

@@ -494,7 +494,7 @@ GetPublicationRelations(Oid pubid, PublicationPartOpt pub_partopt)
 				BTEqualStrategyNumber, F_OIDEQ,
 				ObjectIdGetDatum(pubid));
 
-	scan = systable_beginscan(pubrelsrel, PublicationRelPrrelidPrpubidIndexId,
+	scan = systable_beginscan(pubrelsrel, PublicationRelPrpubidIndexId,
 							  true, NULL, 1, &scankey);
 
 	result = NIL;

src/include/catalog/catversion.h

@@ -53,6 +53,6 @@
  */
 
 /*							yyyymmddN */
-#define CATALOG_VERSION_NO	202112131
+#define CATALOG_VERSION_NO	202201121
 
 #endif

src/include/catalog/pg_publication_rel.h

@@ -42,5 +42,6 @@ typedef FormData_pg_publication_rel *Form_pg_publication_rel;
 
 DECLARE_UNIQUE_INDEX_PKEY(pg_publication_rel_oid_index, 6112, PublicationRelObjectIndexId, on pg_publication_rel using btree(oid oid_ops));
 DECLARE_UNIQUE_INDEX(pg_publication_rel_prrelid_prpubid_index, 6113, PublicationRelPrrelidPrpubidIndexId, on pg_publication_rel using btree(prrelid oid_ops, prpubid oid_ops));
+DECLARE_INDEX(pg_publication_rel_prpubid_index, 6116, PublicationRelPrpubidIndexId, on pg_publication_rel using btree(prpubid oid_ops));
 
 #endif							/* PG_PUBLICATION_REL_H */