Akka.Hosting `LoggerConfigBuilder`

[Aaronontheweb]

Changes

Added some convenience methods for configuring SerilogLogger with Akka.Hosting automatically - and enabling the SerilogLogMessageFormatter to be the default message formatter for the ActorSystem.

Checklist

For significant changes, please ensure that the following have been completed (delete if not relevant):

• [x] This change follows the Akka.NET API Compatibility Guidelines.
• [x] This change follows the Akka.NET Wire Compatibility Guidelines.
• [x] I have reviewed my own pull request.