Create example query on an extension containing a patient attribute

[ianfore]

See the #TODO in search_fhir_patient4.py

A number of patient attributes are recorded as extensions.

A query needs to be formulated which queries for a specific value of a specific patient attribute (extension).

Suggest we do not rely on positional references to extensions in the way I did in the code above. We should be compare this with an example of how this equivalent query would be done in native FHIR e.g. via fhirpy.

      "extension": [
        {
          "url": "http://hl7.org/fhir/us/core/StructureDefinition/us-core-ethnicity",
          "extension": [
            {
              "url": "ombCategory",
              "valueCoding": {
                "system": "urn:oid:2.16.840.1.113883.6.238",
                "code": "2135-2",
                "display": "Hispanic or Latino"
              }
            },
            {
              "url": "text",
              "valueString": "Hispanic or Latino"
            }
          ]
        },
        {
          "url": "http://hl7.org/fhir/us/core/StructureDefinition/us-core-race",
          "extension": [
            {
              "url": "ombCategory",
              "valueCoding": {
                "system": "urn:oid:2.16.840.1.113883.6.238",
                "code": "2106-3",
                "display": "White"
              }
            },
            {
              "url": "text",
              "valueString": "White"
            }
          ]
        }
      ]