Specify which fields can contain markdown

[olinux]

We encountered markdown syntax in some of the "controlled terms" - however, the description of those properties (e.g. "description") in the schema doesn't tell anything about it. From a consumer (and validation) perspective, it would be nice to flag those fields which are containing a specific syntax.

[lzehl]

@olinux in principle we could assume for all strings markdown syntax, no?

[lzehl]

based on our in person discussion we indeed go with the option "_syntax": "markdown" for string values. that way the schema validator will ignore the definition but interpreters such as the KG can use it as a controlled statement for fields that should be interpreted via markdown

[lzehl]

I'll prepare the PR for the respective schemas and let you know when to update the pipeline