Support subscription to different events through one WebSocket connection

[ondrejtomcik]

Feature Request

What is the purpose of the feature?

The goal is to be able to drive what events are received through one WS connection. In the current implementation, the new WS has to be open per each event type and device we are interested in.

What specific challenge does this feature solve?

In case we need to subscribe to resource content changes of 1000 devices, we need to open 1000 WS connections.

What alternatives did I consider?

The gRPC Gateway streams would work, but not on the UI.