PR: Use only POJOs for Jollyday configuratoin to have zero dependencies on Jackson/JAXB or any other xml parsing libraries

[gandulf]

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Hi,
I plan to use jollyday in a quarkus graalvm microservice projects where i try to keep additional dependencies especially regarding jackson/jaxb etc, to a minimum. Therefore I made a jollyday implementation that only uses plain old java objects for configuration.

I know that this means that a change/reconfiguration of the holiday data is no longer possible but in the past years I've been using it I never needed that flexibility since the holiday definitions are rather global and consistent.

Disclaimer: At the moment the POJOs are generated based on the xml files inside a pseudo test class "JavaGeneratorTest" that takes the JacksonConfiguration Classes and creates the POJOs SourceCode using ugly String Writer logic. Not my proudest part of java code, but it works is only needed in case the configuration changes and needs to be recreated.

see PR #451 for current implementation