Improve maven plugin with support for test-jar target

[hsn10]

Dual javadoc jar workflow
We are generating javadoc jars for both source and tests - 2 jars total as part of our standard current maven workflow. Dokka maven plugin supports making jars only from sources.

Describe the solution you'd like
make equivalent of test-jar maven javadoc plugin goal. It should be pretty trivial because you just need to change source and target directory.

[whyoleg]

Thanks for opening the issue! Do you mind explaining the reason why you want to generate a documentation jar for tests?
Are you also open to contributions here?

[hsn10]

because you ship test documentation to project board - they can check what is tested and read test descriptions without giving them high value test suite for passing government standards.