Add attstattarget to FormExtraData_pg_attribute

This allows setting attstattarget when a relation is created.

We make use of this by having index_concurrently_create_copy() copy
over the attstattarget values when the new index is created, instead
of having index_concurrently_swap() fix it up later.

Reviewed-by: Tomas Vondra <tomas.vondra@enterprisedb.com>
Discussion: https://www.postgresql.org/message-id/flat/4da8d211-d54d-44b9-9847-f2a9f1184c76@eisentraut.org

src/backend/commands/indexcmds.c

@@ -1210,7 +1210,7 @@ DefineIndex(Oid tableId,
 					 stmt->oldNumber, indexInfo, indexColNames,
 					 accessMethodId, tablespaceId,
 					 collationIds, opclassIds, opclassOptions,
-					 coloptions, reloptions,
+					 coloptions, NULL, reloptions,
 					 flags, constr_flags,
 					 allowSystemTableMods, !check_rights,
 					 &createdConstraintId);