Add an ability to scan subdirs of Maven and Gradle projects separately

[workshur]

In our case (https://github.com/provectus/kafka-ui), the ReactJS application is part of the maven project / monorepo.
This update allows us to check quality of js app separately.

[marktarry-mobysoft]

We've got a similar issue - where we have a monorepo which also contains a Maven project.

While #29 would technically make it possible to use this action, the change proposed here seems more adaptable to the monorepo use-case.

[akash-jain-10]

We also have the same issue which is block us to us this amazing Github Action for Yarn Project under a Maven Project MonoRepo. Let us know if we can help get this reviewed, merged and published on master! Thanks.

[workshur]

Hello @tom-vanbraband-sonarsource
do you have any suggestions for improvement? How can we promote this PR and get a review?

[tom-vanbraband-sonarsource]

Thanks a lot for your contribution, and apologies for the very late response on our side.
The change looks good!