Co-relating logs

Hi!

At the moment there's no way of co-relating log entries outputted from the handler.
An invocation (without customer log calls would look like:

```

2020-01-14T19:14:17.627+01:00 | Record Handler Progress with Request Id and Request: {RecordHandlerProgressRequest(BearerToken= OperationStatus=IN_PROGRESS, CurrentOperationStatus=PENDING, ClientRequestToken=)}
2020-01-14T19:14:18.283+01:00 | [CREATE] invoking handler...
2020-01-14T19:14:20.304+01:00 | [CREATE] handler invoked
2020-01-14T19:14:20.338+01:00 | Handler returned IN_PROGRESS
2020-01-14T19:14:20.474+01:00 | Record Handler Progress with Request Id and Request: {RecordHandlerProgressRequest(BearerToken=, OperationStatus=IN_PROGRESS, CurrentOperationStatus=IN_PROGRESS, ResourceModel={"attr": 123}, ClientRequestToken=)}
2020-01-14T19:14:20.504+01:00 | Scheduling re-invoke locally after 1 seconds, with Context {RequestContext(invocation=1, callbackContext=CallbackContext(var1=123, var2=321), cloudWatchEventsRuleName=null, cloudWatchEventsTargetId=null)}
2020-01-14T19:14:21.541+01:00 | [CREATE] invoking handler...
2020-01-14T19:14:21.641+01:00 | [CREATE] handler invoked
2020-01-14T19:14:21.667+01:00 | Handler returned SUCCESS
```

The problem at the moment is that we do not have the possibility to co-relate those log entries easily through search.
Is it possible to maybe have the requestId as a prefix to all log entries? or some sort of correlational token like a transactionID?

Thanks!

Das Issue nennt Handler-Aufrufe, Fortschrittsanfragen und lokal geplante erneute Aufrufe, aber keine Dateien oder Tests. Beginnen Sie damit, nachzuverfolgen, wo diese Log-Einträge ausgegeben werden und wie der Aufrufkontext zwischen den Aufrufen weitergegeben wird. Fertig ist die Aufgabe, wenn sich die zugehörigen Einträge zuverlässig anhand eines konsistenten Request- oder Korrelationsbezeichners durchsuchen lassen.

Vom Indexierungsmodell aus dem Issue-Text verfasst.