Mapping the Related Identifier object from DataCite to Schema.org

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This issue hosts the development of the mapping from DataCite to Schema.org for the Related Identifier object. For sake of brevity, we will use the relationType "Cites" to provide a basic structure. Mappings based on other relation types are reserved for another issue.

First, post the correct DataCite xml where all relevant options have been exhausted. Next, post the mapped schema.org result that aligns with this group's format and validates. Also add any modifications needed to the mapping. Then, iterate with those interested towards a final result.

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The XML from DataCite's documentation for the RelatedIdentifier object, reduced to only contain the "Cites" relationType as instructed above, but extended to include a worst case scenario where only a URL is known:

<relatedIdentifiers>
    <relatedIdentifier relatedIdentifierType="DOI" relationType="Cites" resourceTypeGeneral="JournalArticle">10.21384/bar</relatedIdentifier>
    <relatedIdentifier relatedIdentifierType="URL" relationType="Cites" >https://github.com/ESIPFed/science-on-schema.org/blob/main/guides/Dataset.md</relatedIdentifier>
</relatedIdentifiers>

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The proposed output below faces the challenge of what to do when
"https://" + relatedIdentifierType + ".org" + value
does not result in an operating PID-based URL, with the exception of when the relatedIdentifierType = "URL". A related logic to check here is what happens when
"https://registry.identifiers.org/registry/" + relatedIdentifierType (other than URL)
also does not result in an operating URL.
Note that the fields included below for relatedIdentifierType="URL" are different than for DOIs.

{
   "@context": {
      "@vocab": "https://schema.org/"
   },
   "@type": "Dataset",
   "citation": [
      {
         "@id": "https://doi.org/10.21384/bar",
         "@type": "ScholarlyArticle",
         "identifier": {
         	"@id": "https://doi.org/10.21384/bar",
            "@type": "PropertyValue",
            "propertyID": "https://registry.identifiers.org/registry/doi",
            "url": "https://doi.org/10.21384/bar",
            "value": "doi:10.21384/bar"
         }
      },
      {
         "@id": "https://github.com/ESIPFed/science-on-schema.org/blob/main/guides/Dataset.md",
         "@type": "CreativeWork",
         "identifier": {
         	"@id": "https://github.com/ESIPFed/science-on-schema.org/blob/main/guides/Dataset.md",
            "@type": "PropertyValue",
            "url": "https://github.com/ESIPFed/science-on-schema.org/blob/main/guides/Dataset.md",
         }
      }
   ]
}