Event externalization bootstrap should log which event types it's configured to externalize.

[odrotbohm]

trafficstars

The analysis of this sample project here made obvious, that it's difficult to detect that events from modules not included in test runs are not subject to application module scoped integration tests. A simple log message that describes which events are selected for externalization.

We should add a bit of debug-level logging to help to diagnose such problems.