Separate exceptions logging and retries configuration

[EloiZalczer]

Actors use the throws argument to configure expected errors.
This argument is then used in WorkerThread to format logging and in Retries to schedule or abort messages.

In my case, I want to be able to define expected exceptions, so that they aren't logged with a full stack trace, but I still need the messages to be retried when the actor fails.

Here are some possible solutions I can think of:

• Add a new argument retry_on_expected, with a default value of False to avoid breaking retro-compatibility.
• Use two different arguments to configure exceptions that should be logged as info and exceptions that should not trigger a retry (would break retro-compatibility).
• Add a way to configure logging in the worker without changing Actor arguments.

Would you be open to this change ? I would be glad to open a PR with whichever solution is preferred.