Reduce technical debt

There are some code aspects of the provisioning app that we need to improve. Goals of this issue are to clean up some antipatterns, improve unit tests, improve code readability, update dependencies, etc.

This is a preliminary list for ODS Prov App 4.x:

• All spring test should only use spring support and not a mix of spring and mockito (no @InjectMocks, etc)
• Fix encapsulation of all classes, no protected properties -> getter and setters
• Remove critical circular dependencies
• Update Dependencies (snyk findings) und spring boot
• Fix Sonarqube findings (ev. sonarqube in .github action enable)
• Update to latest gradle v6.7.1 and remove deprecated gradle features
• Remove @author
• Remove deprecated classes like ProjectData
• etc...