Feature Request: Build targets to run with Shenandoah and ZGC

[leadVisionary]

Great work with your plugin. I've used it successfully to write a benchmark on serialization libraries and corresponding report.

It's fairly trivial to make a benchmark run with Shenandoah or ZGC...but it's kind of a pain to do it manually in a build.gradle every time I want to swap between the two or go back to G1.

The obvious answer to me is a separate build target, but my Gradle foo is not super great for customizations. If the necessary incantations are obvious to you (with your pretty deep experience in Gradle), it would be great if you could add them to the plugin...or even just add a Gist here for posterity.