Schema automator for OMOP: concept_class_id falsely inferred as idenitifier

[matentzn]

See #98

When trying to infer the schema for all OMOP tables, concept_class_id is inferred to be an identifier, while this should be a foreign key (or nothing).

concept_class_id:
    examples:
    - value: RNA Variant
    from_schema: https://w3id.org/omop_vocabulary
    identifier: true
    range: string