Citation for Product / Patent entities

[floriangantner]

Is your feature request related to a problem? Please describe.
The implementation of the citation / csl generation is hardly restricted to the Publication entity.

Describe the solution you'd like
We would like the citation also be available for other research outcomes like Product or Patent.
Document types of these entities are supported in the current citeproc dependency
https://github.com/michel-kraemer/citeproc-java/blob/master/citeproc-java/templates/CSLType.json

Depending on the entity type it should be possible to define multiple DSpaceListItemDataProvider with slightly different mapping for every entity type.

Describe alternatives or workarounds you've considered
show no citation.

Additional context

• without this feature there is no bibtex in orcid push of product entities or patent entities