[MNG-6454] Introduce option to allow non-pom packaging types to also support the modules-tag

**[Robert Scholte](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=rfscholte)** opened **[MNG-6454](https://issues.apache.org/jira/browse/MNG-6454?redirect=false)** and commented

While working on the multirelease jars I noticed we're missing a feature in Maven. At JCrete after talking with [sanne](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=sanne) he had a similar request for a different reason. In his case it is about having a jar where all Drivers are optional, so developers only have to add this jar. However, it would be great it code could be isolated per Driver.

The idea is to allow packaging:jar to specify modules in the pom. These submodules follow the normal lifecycle, but are never installed or deployed. Instead the root-project will embed these files in the main jar.

To support this, Maven first of all recognize if modules are allowed for a specific packaging type. The `org.apache.maven.artifact.handler.ArtifactHandler` looks close, but that should be about artifacts (dependencies). So most likely we need a new ProjectHandler here.

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No further details from [MNG-6454](https://issues.apache.org/jira/browse/MNG-6454?redirect=false)