data models for custom notification are out dated

[djs0109]

Is your feature request related to a problem? Please describe.
Orion has updated the behavior of custom notifcation. Users can define more flexible notification to forward data to external endpoint.

Describe the solution you'd like
New features should include (but not limited to):

• filip support right now only paylaod in mqttCustom/httpCustom, but Orion already supports json and ngsi as further options. #288
• Macro substitution for templates is also supported, e.g., ${service} is replaced by the service #297
• httpCustom.headers #290
• covered field for more general notifications that cover multiple entity types, see here #298
• alterationTypes as stated in Support of alterationTypes in subscriptions #198