Add support for Gradle multi-module projects.

[CristianGM]

The approach to inject the plugin dependency-license-report plugin used here is making a modified copy of the build.gradle and running it with -b, it means Gradle will ignore the settings.gradle and ignore all the subprojects (modules).

I asked on Gradle Slack and they told me to use an init script instead so it works properly, that will also fix the issue that we are only considering build.gradle and not the "new" build.gradle.kts which would change the syntax slightly.

Alternatively it would be possible to copy the settings.gradle to another file adding to it rootProject.buildFileName = "license-....gradle"´ and using it adding to the cli -c licensed-settings.gradle, but then we still need to add support for .gradle.kts files

[jonabc]

@CristianGM I don't have deep knowledge of Gradle, but am happy with any changes that maintain backwards compatibility while solving the problems you mention. Would you be able to open a PR?

[jonabc]

This was resolved with #583, which will be part of the major version 4.0 release