Feature: support for minQuantity and maxQuantity extensions

[robeastwood-agency]

Describe the solution you'd like
Requesting that for items of type quantity that support be provided for the 2 associated SDC extensions

• http://hl7.org/fhir/uv/sdc/StructureDefinition/sdc-questionnaire-minQuantity
• http://hl7.org/fhir/uv/sdc/StructureDefinition/sdc-questionnaire-maxQuantity

The result of this would be that the lower and upper bounds for a given quantity item would be controlled.

Describe alternatives you've considered
none available

Additional context
Refer to issue #639

Example item:

{
      "extension": [
        {
          "url": "http://hl7.org/fhir/StructureDefinition/questionnaire-unitOption",
          "valueCoding": {
            "system": "http://unitsofmeasure.org",
            "code": "kg",
            "display": "kg"
          }
        },
        {
          "url": "http://hl7.org/fhir/uv/sdc/StructureDefinition/sdc-questionnaire-minQuantity",
          "valueQuantity": {
            "value": 0,
            "system": "http://unitsofmeasure.org",
            "code": "kg"
          }
        },
        {
          "url": "http://hl7.org/fhir/uv/sdc/StructureDefinition/sdc-questionnaire-maxQuantity",
          "valueQuantity": {
            "value": 300,
            "system": "http://unitsofmeasure.org",
            "code": "kg"
          }
        }
      ],
      "linkId": "body-weight",
      "type": "quantity",
      "text": "Body Weight"
}