Make javadoc and sources optional when publishing/exporting to maven (per-target)

Seen javadoc process consuming lots of cpu&mem, also just a matter of being able to customize what's exported.
Disabling should disable not only publishing but also building sources/javadocs.

Start by tracing the repository's Maven publishing and export configuration, then identify where per-target options are defined. Verify how javadocs and sources are built and published; done means each target can disable them for both building and publishing.

Written by the indexing model from the issue text.