Align event-subscriptions with updated design guidelines based on CloudEvents

**Problem description**
After approving [PR56 Update DG with use of callbacks & cloudEvents](https://github.com/camaraproject/Commonalities/pull/56) the DeviceStatus API definition needs to be updated too.

**Expected behavior**
Update the event-subscription related parts in the API spec based on the updated DG


**Alternative solution**


**Additional context**

