anchor.diff:                  },
                   "notification": {
                       "callback": "http://localhost:1234",
  +                    "headers": {
  +                      "X-MyHeader": "foo"
  +                    },
  +                    "query": {
  +                      "authToken": "bar"
  +                    },
  +                    "attrsFormat": "keyValues",
  +                    "dataFormat": "object",
                       "attributes": ["temperature", "humidity"],
                       "throttling": 5,
                       "count": 12,
  
positive.code: * If there is more than one attribute exposing location which has been labeled as being the
  *default location*, then the query will be declared as ambigous and an HTTP error response with code ``409``
  must be sent. 
  
  ## Group API Entry Point
  
  
negative.code: A `notification` object contains the following subfields:
  
  + `attributes`: List of attributes to be included in the notification message. If not specified (or empty), all attributes are included
    in the notification. It also defines the order in which attributes will appear in notifications when `attrsFormat` "value" is used
    (see "Notifications formats") section.
  + `callback` : URL pointing to the service which will be invoked when a notification is generated. A NGSIv2
    compliant server must support `http` URL schema, other schemas (e.g. schemas for web sockets) could also be supported.
  + `headers`: a key-map of HTTP headers that will be included in the notification messages.
  + `query`: a key-map of URL query parameters that will be included in the notification message.
  + `attrsFormat`: specifies how the attributes will be represented in notification. See detail in "Notifications format section".
  + `dataFormat`: specifies how data will be represented in notifications. See detail in "Notifications format" section.
  + `throttling`: Minimal period of time in seconds which must elapse between two consecutive notifications. It
    is optional.
  + `timesSent` (not editable, only in GET operations): Number of notifications sent due to this subscription.
  