Insert metadata in (dataset) pages, for (google)datasetsearch

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Is your feature request related to a problem? Please describe.
I would like to find clowder datasets in https://datasetsearch.research.google.com/ and via other aggregators

Describe the solution you'd like
Insert json-ld into at least the dataset pages, and then an associated entry in the sitemap, so it can be crawled

Describe alternatives you've considered
Given the possibly very large numbers, we need to give just enough metadata to get in the right area, and then be able to follow the Linked-Data follow your nose pattern. This might mean allowing for (api) calls to get the file/etc metadata as needed.

Additional context
This will be done in stages, starting with the mapping of the dataset and file classes, which is in a draft-PR

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sitemap will come later, as well as some of the other possible metadata
Right now just starting w/two classes: File and Dataset, to product jsonld describing their attributes mapped to schema.org vocabulary terms In the end the two *.scala.html outputs can be taken from the output html and pasted into: https://validator.schema.org to that once the sitemap is there, all of those elements from the linked Datasets could end up in https://datasetsearch.research.google.com/

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Dataset Files and the classes they hold instances of, all have to_jsonld methods, that get kicked off in the view; only other change was to signature of Utils.baseURL

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After this is accepted, the next step is issue #351 to get the sitemap so the datasets can get crawled

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pr comments have been closed for awhile, also not much sitemap feedback, so will look at other issues too