Add metadata id in response when GET metadata from dataset and file

[longshuicy]

Is your feature request related to a problem? Please describe.
GET /api/files/{id}/metadata.jsonld
GET /api/datasets/{id}/metadata.jsonld
the response of above two endpoints do not include metadata id; when working on the React frontend, in order to properly delete a metadata, we need that metadata id in the response

Describe the solution you'd like
here is an example of the current response:

[
    {
        "@context": [
            "https://clowderframework.org/contexts/metadata.jsonld",
            {
                "csv_headers": "http://clowder.ncsa.illinois.edu/metadata/ncsa.csvheaders"
            }
        ],
        "attached_to": {
            "resource_type": "cat:file",
            "url": "https://clowder.ncsa.illinois.edu/clowder/files/610d55745e0e9253e6586490"
        },
        "created_at": "Fri Sep 17 14:47:20 GMT 2021",
        "agent": {
            "@type": "cat:extractor",
            "name": "https://clowderframework.org/clowder/extractors/ncsa.csvheaders/1.0",
            "extractor_id": "https://clowderframework.org/clowder/extractors/ncsa.csvheaders/1.0"
        },
        "content": {
            "csv_headers": [
                "Site_ID",
                "Date&Time",
                "Discharge(cms)"
            ]
        }
    }
]

proposing to add a id field there

Describe alternatives you've considered
NA

Additional context
probably we need to do something in here

 def getExtractedMetadataByAttachTo(resourceRef: ResourceRef, extractor: String): List[Metadata] = {
    val regex = ".*extractors/"+extractor

    val order = MongoDBObject("createdAt" -> -1)
    MetadataDAO.find(MongoDBObject(
      "attachedTo.resourceType" -> resourceRef.resourceType.name,
      "attachedTo._id" -> new ObjectId(resourceRef.id.stringify),
      // Get only extractors metadata even if specific extractor not given
      "creator.extractorId" -> (regex).r
    )).sort(order).toList
  }