add uri reference which is populated from dataseturi or uricode

[pvgenuchten]

Overview

This adds datasetUri / uricode as a uri property to pycsw, then adds it as a link to ogc-api records

Related Issue / Discussion

geopython/OWSLib#946

Additional Information

Contributions and Licensing

(as per https://github.com/geopython/pycsw/blob/master/CONTRIBUTING.rst#contributions-and-licensing)

• I'd like to contribute [feature X|bugfix Y|docs|something else] to pycsw. I confirm that my contributions to pycsw will be compatible with the pycsw license guidelines at the time of contribution.
• I have already previously agreed to the pycsw Contributions and Licensing Guidelines

[pvgenuchten]

welcoming your thoughts, i still have to fix tests (demo server is failing now and then)