[MSHARED-389] create an IT to show how to write a reporting mojo that uses external generator

[jira-importer]

Hervé Boutemy opened MSHARED-389 and commented

latest questions on maven-dev and looking at m-javadoc-mojo, I think that a little demo would help

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Affects: maven-reporting-impl-2.3

[jira-importer]

Hervé Boutemy commented

done in r1643698