Update publish plugin to expose an API for using pre-existing pom file

[bjhargrave]

Expected Behavior

When wanting to publish an already built gradle plugin artifact in the Plugin portal, you want to use the existing pom file. See #9 (comment).

The pluginBundle DSL should provide a way to use the existing pom file (either as a supplied file or as the pom resource in the artifact jar) rather than always generating a new pom file.

Current Behavior

The publish plugin always generates a new pom file which will not contain necessary information already in the existing pom file.

Context

See #9.

[lacasseio]

Thanks for opening this issue. It's great feature to have. It may overlap with some of the work around using the maven-publish and the variant aware publishing that we are discussing but it's definitely something that should be doable from the plugin author.

[JLLeitschuh]

You can absolutely hack this to make it work (I've done so in the past for some testing) but I agree we should expose an official way to do this.

[marcphilipp]

FWIW I've submitted a workaround to bnd: bndtools/bnd#3811