sqldb+graph/db: update FilterKnownChanIDs to use pagination

Remove a TODO by making use of the new sqldb.ExecutePagedQuery to fetch
channels in batches rather than one by one.

sqldb/sqlc/queries/graph.sql

@@ -231,6 +231,11 @@ WHERE scid >= @start_scid
 SELECT * FROM graph_channels
 WHERE scid = $1 AND version = $2;
 
+-- name: GetChannelsBySCIDs :many
+SELECT * FROM graph_channels
+WHERE version = @version
+  AND scid IN (sqlc.slice('scids')/*SLICE:scids*/);
+
 -- name: GetChannelsByOutpoints :many
 SELECT
     sqlc.embed(c),