Support multi-module maven projects

[ckunki]

For project-keeper ARCM reports error

er-root: Execution default-cli of goal com.exasol:artifact-reference-checker-maven-plugin:0.4.1:unify failed: 
E-ARCM-5: The project configured non of the following jar-building plugins: [maven-assembly-plugin, maven-shade-plugin]. 
Other methods of building a jar file are currently not supported. Known mitigations:
[ERROR] * Please check your project's configuration
[ERROR] * Open a ticket at the artifact-reference-checker-maven-plugin to add support for different jar-building plugins.