feat: add module info

[dizney]

• add moditect maven plugin to generate module-info.java, which excludes the internal package from exporting
• updated example project to use newer maven compiler which supports modules, and add a module-info.java to require the dotenv module

Resolves #20

[dizney]

I used io.github.cdimascio.dotenv.java as module name which might be up for debate. I mainly added the .java to differentiate it from the dotenv-kotlin module/package.

[cdimascio]

@all-contributors add @dizney for code and doc

[allcontributors]

@cdimascio

I've put up a pull request to add @dizney! 🎉