Using "use" attributes of the ruleset in TitleGenerator instead of fixed fields

[markusweigelt]

Is your feature request related to a problem? Please describe. In the ruleset, there are the attributes use="authorLastName", use="title", use="processTitle". TitleGenerator should use these attributes instead of fixed field names for generation. In addition, the TSL_ATS and TITLE_DOC_MAIN constants of TitleGenerator should be refactored to use more generic and suitable "use" attribute of ruleset.

Describe the solution you'd like When fixing this issue, it should be done in a way that the values of the metadata entries marked use="authorLastName" and use="title" should be used as the source for the ATS/TSL creation, and the generated ATS/TSL should be written into any metadata fields tagged use="processTitle".