Ensure SO:creator is processed as a @list

[gothub]

In order to index SO:creator properly, it has to be represented in the JSON-LD document as a @list.

Should an error be generated if SO:creator is not typed as a list, or should the harvesting update the incoming document to add this type if not present?

See

• Index JSON-LD documents containing SO:Dataset descriptions d1_cn_index_processor#3
• Preserving item order where needed ESIPFed/science-on-schema.org#135