[MNG-6876] ExecutionEvent/EventSpy

**[Nick Cross](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=rnc)** opened **[MNG-6876](https://issues.apache.org/jira/browse/MNG-6876?redirect=false)** and commented

Provide more detailed documentation on the ExecutionEvent and https://maven.apache.org/examples/maven-3-lifecycle-extensions.html so its clear when certain 'phases' / 'hooks' are called e.g.
* if a dependency is scope import when is it resolved ?
* Difference between session start in AbstractMavenLifecycleParticipant and AbstractExecutionListener ?
* I have found https://dev-maziarz.blogspot.com/2015/03/maven-323-internals-how-it-works.html and https://github.com/khmarbaise/test-maven-eventspy but it would be nice to have internal documentation/examples which demonstrate this.

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