Return GeoJSON FeatureCollection from stations list API endpoint

[ricardogsilva]

This PR changes the default response type of /api/v2/observations/stations (AKA the stations list endpoint) to be a GeoJSON feature collection.

The proposed implementation makes the default response media type be application/geo+json. It is still possible to get the previous response type by simply passing the accept header Accept: application/json - we can decide later if it is worth keeping the plain JSON response or just have the GeoJSON.

The response payload is modeled after the response produced by pygeoapi's collection items endpoint for OGC API Features, with some small tweaks:

• renamed numberMatched and numberReturned to number_matched and number_returned
• added number_total
• for brevity, the main links contents is an object of simple key: value links, we may change to a list of proper Link types later
• added links to each feature

Example request using the httpie client (the limit query parameter is passed just for getting a small response that I can paste here:

http localhost:5001/api/v2/observations/stations limit==2

and corresponding response

{
  "type": "FeatureCollection",
  "features": [
    {
      "type": "Feature",
      "geometry": {
        "type": "Point",
        "coordinates": [
          12.28232702,
          45.88132477
        ]
      },
      "properties": {
        "code": "100",
        "name": "Conegliano",
        "type_": "agro",
        "altitude_m": 90
      },
      "id": "4eb8a422-22f1-4bd5-827d-763ba84891f0",
      "links": [
        "http://localhost:5001/api/v2/observations/stations/4eb8a422-22f1-4bd5-827d-763ba84891f0"
      ]
    },
    {
      "type": "Feature",
      "geometry": {
        "type": "Point",
        "coordinates": [
          12.36910037,
          44.9173386
        ]
      },
      "properties": {
        "code": "101",
        "name": "Porto Tolle - Pradon",
        "type_": "agro",
        "altitude_m": -3
      },
      "id": "72d079c3-b071-4e31-87e7-bcebafc0d220",
      "links": [
        "http://localhost:5001/api/v2/observations/stations/72d079c3-b071-4e31-87e7-bcebafc0d220"
      ]
    }
  ],
  "links": {
    "self": "http://localhost:5001/api/v2/observations/stations?limit=2&offset=0",
    "next": "http://localhost:5001/api/v2/observations/stations?limit=2&offset=2",
    "previous": null,
    "first": "http://localhost:5001/api/v2/observations/stations?limit=2&offset=0",
    "last": "http://localhost:5001/api/v2/observations/stations?limit=2&offset=182"
  },
  "number_matched": 182,
  "number_total": 182,
  "number_returned": 2
}

---

• fixes #66