graph/db+sqldb: batch validation for zombie index migration

Finally, we update the migrateZombieIndex function to use batch
validation just like was done in the previous commits. Here, we
additionally make sure to validate the entire zombie index entry and not
just the SCID.

sqldb/sqlc/queries/graph.sql

@@ -908,6 +908,12 @@ DO UPDATE SET
     node_key_1 = COALESCE(EXCLUDED.node_key_1, graph_zombie_channels.node_key_1),
     node_key_2 = COALESCE(EXCLUDED.node_key_2, graph_zombie_channels.node_key_2);
 
+-- name: GetZombieChannelsSCIDs :many
+SELECT *
+FROM graph_zombie_channels
+WHERE version = @version
+  AND scid IN (sqlc.slice('scids')/*SLICE:scids*/);
+
 -- name: DeleteZombieChannel :execresult
 DELETE FROM graph_zombie_channels
 WHERE scid = $1