The current version of readthedocs is missing the uml diagrams as well as the latest version of PSDM (2.0.0). This should be updated - [x] update [gettingStarted](https://github.com/ie3-institute/PowerSystemDataModel/blob/dev/docs/readthedocs/gettingstarted.rst) with latest maven dependency - [x] add a specific section for uml diagrams - [x] add uml diagrams in the newly created section