No support for custom properties in incident api

[nathanielbrakeley]

Per the docs: https://docs.opsgenie.com/docs/incident-api#add-detailscustom-properties-to-incident there should be support for adding/removing custom properties on incidents, but this is not currently implemented in the api. It looks like there is support on the Incident object, but the API returns a "No handler found" if you try to use the endpoint in the docs.