OAI_ORE exporter media type should be application/ld+json

From https://dataverse.harvard.edu/api/info/exportFormats it's hard to tell which formats are based on JSON-LD. Only one of three (schema.org) is clearly application/ld+json:

{
  "status": "OK",
  "data": {
    "OAI_ORE": {
      "displayName": "OAI_ORE",
      "mediaType": "application/json",
      "isHarvestable": false,
      "isVisibleInUserInterface": true
    },
...
    "schema.org": {
      "displayName": "Schema.org JSON-LD",
      "mediaType": "application/ld+json",
      "isHarvestable": false,
      "isVisibleInUserInterface": true
    },
...
    "croissant": {
      "displayName": "Croissant",
      "mediaType": "application/json",
      "isHarvestable": false,
      "isVisibleInUserInterface": true
    },
...
}

For croissant I opened this pull request (it also adds a profile, like this: application/ld+json; profile="http://mlcommons.org/croissant/1.0"):

• https://github.com/gdcc/exporter-croissant/pull/7

Should we make a similar change for OAI_ORE? The spec at https://www.openarchives.org/ore/0.9/jsonld seems to prefer application/ld+json:

As a side note, it might be interesting to show which formats are based on Schema.org.

Start at the /api/info/exportFormats entry point and trace the OAI_ORE format definition. Confirm the OAI ORE specification's preferred media type, update the reported value to application/ld+json, and verify that the endpoint output identifies OAI_ORE accordingly.