Enhance language around IS-04 version update

[garethsb]

In the Controller spec document we now have:

The Controller SHOULD use an IS-04 Query API WebSocket connection to monitor version timestamp increments on Senders and Receivers being controlled.

In Interoperability: IS-04: Discovery, it's mentioned that Devices advertise the Connection API and that when parameters of Senders or Receivers change, their IS-04 version is updated.

We think something needs to advertise when particular Senders or Receivers are added or removed from IS-05. This could be the IS-04 Sender or Receiver version (reflecting the presence/absense of the /x-nmos/connection/v1.1/senders/{senderId} URL path) or the Device version (reflecting the change to the /x-nmos/connection/v1.1/senders response).

[peterbrightwell]

Architecture Review Group review: place on backlog