logging assembly discovery

#1562
We might want to add more data here - there's a few dimensions for filters:

1. An `IFilter` might be either, pure metadata, or an `IFilterFactory`, or an implementation of one of our predefined filter interfaces (like `IActionFilter`)
2. If it's an `IFilterFactory` we might want to special case `TypeFilterAttribute` and `ServiceFilterAttribute` - in these cases we can show the 'real' filter
3. If it's an implementation of one or more filter interfaces, we probably want to communicate that info.