[REQ] [JavaSpring] Support for generating gradle files in Java Spring

Created by: penghez

Is your feature request related to a problem? Please describe.

Hi team, can we provide some options to generate build.gradle & settings.gradle with Spring templates? It might be helpful for some gradle projects to use the generated project as a sub-project if we can provide gradle file there.

Describe the solution you'd like

I also see the current Java template has already got a gradle.mustache. Can we bring something similar in the JavaSpring? Thank you so much.

Additional context

Similar issue also raised in Swagger-generator Issue 668

Thank you, the generator really helps a lot!