[improve][broker] Change log level from warn to debug when cursor mark-deleted position ledger doesn't exist (#25200)

Author: Shawyeok

managed-ledger/src/main/java/org/apache/bookkeeper/mledger/impl/ManagedLedgerImpl.java

@@ -2618,7 +2618,8 @@ public CompletableFuture<Void> maybeUpdateCursorBeforeTrimmingConsumedLedger() {
                     log.debug("No need to reset cursor: {}, current ledger is the last ledger.", cursor);
                 }
             } else {
-                log.warn("Cursor: {} does not exist in the managed-ledger.", cursor);
+                // It's possible that the ledger at the mark-deleted position is empty and has been deleted already.
+                log.debug("Cursor: {} mark-deleted position ledger does not exist in the managed-ledger.", cursor);
             }
 
             int compareResult = lastAckedPosition.compareTo(markDeletedPosition);