Improve EDR metadata for parameters

[maartenplieger]

Currently the EDR service returns the following for parameters (i18n was removed??):
(From https://geoservices.knmi.nl/edr/collections )

{
  "air_temperature_hagl": {
    "type": "Parameter",
    "id": "air_temperature_hagl",
    "label": "air_temperature_hagl",
    "unit": {
      "symbol": "C"
    },
    "observedProperty": {
      "id": "air_temperature_hagl",
      "label": "air_temperature_hagl"
    }
  }
}

Could it be adjusted towards:

{
  "air_temperature_hagl": {
    "type": "Parameter",
    "description":"HAP1(NL) Air temperature at 2 m",
    "id": "air_temperature_hagl",
    "label": "air_temperature_hagl",
    "unit": {
      "label": "degree Celsius",
      "symbol": {
        "value": "°C",
        "type": "http:https://www.opengis.net/def/uom/UCUM/"
      }
    },
    "observedProperty": {
      "id": "https://vocab.nerc.ac.uk/standard_name/air_temperature/",
      "label": "Air temperature"
    }
  }
}

Question: Do we really need id, label and unit.label ?
We need to check the covjson spec on the distinction between id, label and description

Description could be obtained from the WMS title in the WMS GetCapabilities
Suggested EDR config could be:

 <EdrParameter name="air_temperature_hagl" unit="°C" standard_name="air_temperature" label="Air temperature, 2 metre"/>

(Label TBD)