Create JSKOS-API Backend

[nichtich]

To access JSKOS Server instances and DANTE Terminology provider:

• add BackendType and TargetDbSchema jskos
• implement org.semantics.apigateway.api.JskosTransformer
• add case here in transformJsonResponse (and maybe refactor to not use switch/case anyway if each case has same pattern)
• maybe add something in https://github.com/ts4nfdi/api-gateway/tree/main/src/main/resources (not sure about the role of this files) and in AggregatedResourceBody
• add default JSKOS databases: https://api.dante.gbv.de/ and https://coli-conc.gbv.de/api/ (see /status of each for individual capabilities)
• add unit tests