MNT: Delay packet downloader cron job

The POC has indicated that there could be a delay between when the
file arrives and when it gets ingested and available in the database.
I think this means there could still potentially be a further delay
so lets not push it too close to the 0/6/12/18 boundaries and give
it 20 minutes buffer to fill the database after each request.

Author: greglucas

sds_data_manager/constructs/packet_downloader_lambda_construct.py

@@ -100,8 +100,8 @@ def __init__(
         rule = aws_events.Rule(
             self,
             "PacketDownloaderScheduleRule",
-            # Every 6 hours at 5 minutes past the hour
+            # Every 6 hours at 20 minutes past the hour
             # 00:00 -> 06:00, 06:00 -> 12:00, 12:00 -> 18:00, 18:00 -> 00:00
-            schedule=cdk.aws_events.Schedule.cron(minute="5", hour="*/6"),
+            schedule=cdk.aws_events.Schedule.cron(minute="20", hour="*/6"),
         )
         rule.add_target(cdk.aws_events_targets.LambdaFunction(packet_lambda))