Stream entity events

Establishes a server-sent events (SSE) connection that streams entity data in real-time. This is a one-way connection from server to client that follows the SSE protocol with text/event-stream content type. This endpoint enables clients to maintain a real-time view of the common operational picture (COP) by first streaming all pre-existing entities that match filter criteria, then continuously delivering updates as entities are created, modified, or deleted. The server first sends events with type PREEXISTING for all live entities matching the filter that existed before the stream was open, then streams CREATE events for newly created entities, UPDATE events when existing entities change, and DELETED events when entities are removed. The stream remains open indefinitely unless preExistingOnly is set to true. Heartbeat messages can be configured to maintain connection health and detect disconnects by setting the heartbeatIntervalMS parameter. These heartbeats help keep the connection alive and allow clients to verify the server is still responsive. Clients can optimize bandwidth usage by specifying which entity components they need populated using the componentsToInclude parameter. This allows receiving only relevant data instead of complete entities. The connection automatically recovers from temporary disconnections, resuming the stream where it left off. Unlike polling approaches, this provides real-time updates with minimal latency and reduced server load.