update distributed search functionality

[tomkralidis]

Overview

This PR updates distributed search functionality as follows:

• updates OGC API - Records based implementation to OGC API - Records - Part 4: Federated Search (draft)
• implements "qualified" distributed search, allow configuration to specify various distributed catalogue types (OARec, CSW, STAC API)

Related Issue / Discussion

None

Additional Information

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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