Minimal environment for creating a language override plugin

[judgej]

There are some small changes we need to make to the output generator, the final language override stage. A custom override I guess is what we need (which could possibly extend org.openapitools.codegen.languages.AbstractPhpCodegen or even org.openapitools.codegen.languages.PerlClientCodegen since these should be only minor tweaks.

I understand we can add a jar file of these classes or class as plugin at runtime. I have never coded Java before, so don't have any environments set up, but adding a few lines of code looks simple enough. What is the minimal that can be set up that will allow me to tweak a java file and spit out a suitable jar file that I can use as a generator plugin? Is there perhaps a container I can use already set up to compile customisation plugins?

@bradydan