adding NULLS LAST in desc index on lineage_events.created_at

Signed-off-by: Prachi Mishra <prachi.mishra@astronomer.io>

api/src/main/resources/marquez/db/migration/V54__lineage_events_created_at_indexed.sql

@@ -1,7 +1,7 @@
 -- new column will be created with 'null' filled for existing rows
 ALTER TABLE lineage_events ADD created_at TIMESTAMP WITH TIME ZONE;
 
-create index lineage_events_created_at_index on lineage_events (created_at desc);
+create index lineage_events_created_at_index on lineage_events (created_at desc NULLS LAST);
 
 -- The new default set to UTC now() will only apply in subsequent INSERT or UPDATE commands; it does not cause rows already in the table to change.
 ALTER TABLE lineage_events ALTER COLUMN created_at SET DEFAULT (now() AT TIME ZONE 'UTC')::timestamptz;