anchor.diff:  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
  +  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.
  
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:                 },
                  "notification": {
                      "callback": "http://localhost:1234",
                      "headers": {
                        "X-MyHeader": "foo"
                      },
                      "query": {
                        "authToken": "bar"
                      },
                      "attrsFormat": "keyValues",
                      "dataFormat": "object",
                      "attributes": ["temperature", "humidity"],
                      "throttling": 5,
                      "count": 12,
  