Adding facets and facet extensibility

[pbuttigieg]

Facets in our search UX are represented in the following ways:

These are primarily defined by the @type of the record (Dataset, Person, Project, etc), but can also be defined by the @type and other metadata in a JSON-LD file (e.g. a "Method" could be a Document, image, video, or other form of multimedia that has a keyword "method" [we'll define these]).

• The updated UI should have new facets added, corresponding to the new @types we've added to the backend (we'll define the list).
• Further - this list should be easy to extend using a config file approach: The maintainer would just need to add the name of the facet, the link to the icon for the UI, and a link to the query needed to populate the facet