Feature request: Exclude packages / directories

I use [JHipster](https://www.jhipster.tech/) which generates a Spring Boot / Angular project for me. Now I don't want to format the generated code I never touch. That's why I need to exclude Java packages/directories from formatting.

I believe I can do this in the Google Java Format Gradle plugin. I'd like to exclude Java packages/directories in the IntelliJ plug-in, too.