schema for i18n strings

[lueck]

Schemas for i18n strings must be written. This type should be alternative types like in typescript type i18n = string | LanguageMap | LanguageArray

These types must work for these JSON-LD types:

• strings
• Language Maps
• the example for dublinCore.title in the DTS specs, which we should call LanguageArray

Migrated from GitLab: https://zivgitlab.uni-muenster.de/SCDH/apis/dts-openapi-specs/-/issues/5

[lueck]

set status to To do