Catalog Publisher not configurable

[dev-rke]

Hey,

when using the validator against dcat-ap.de version 2.0, it seems currently impossible to define the publisher of a catalog.
As this is a required setting to have a valid schema, and the validator mentioned that, it might be worth adding a configuration setting via this extension.

More details, see here:
https://www.dcat-ap.de/def/dcatde/2.0/spec/#katalog-herausgeber
https://www.dcat-ap.de/def/dcatde/3.0/spec/#katalog-herausgeber

[toothstone]

@dev-rke Here is what I implemented as a quick fix: https://gitlab.opencode.de/connected-urban-twins/cut-leipzig-open-data-portal/ckanext-odp-le-profile/-/merge_requests/4