sub schema (SchemaAttributePathInstance) domain model extension + test re-factoring

* incl. new init_internal_schema.sql script (+ generation via code)
It looks like that something with the (commits of the) MR is wrong. https://github.com/zazi/dswarm/blob/sprint-24/dd-701/persistence/src/test/java/org/dswarm/persistence/service/schema/test/internalmodel/BiboDocumentSchemaBuilder.java shows also the outdated code. however, https://github.com/zazi/dswarm/blob/sprint-26/dd-734/persistence/src/test/java/org/dswarm/persistence/service/schema/test/internalmodel/BiboDocumentSchemaBuilder.java should include the actual version of it.