Drop older slots in the ledger (#5188)

* Add facility to delete blocktree columns in range

* Add ledger cleanup service

* Add local_cluster test

core/src/lib.rs

@@ -42,6 +42,7 @@ pub mod gossip_service;
 pub mod leader_schedule;
 pub mod leader_schedule_cache;
 pub mod leader_schedule_utils;
+pub mod ledger_cleanup_service;
 pub mod local_cluster;
 pub mod local_vote_signer_service;
 pub mod packet;