Add websocket event stream for sim updates.

As a proof of concept this only covers the flight positions.

game/server/eventstream/routes.py

@@ -0,0 +1,21 @@
+from fastapi import APIRouter
+from fastapi.encoders import jsonable_encoder
+from starlette.websockets import WebSocket
+
+from .eventstream import EventStream
+from .models import GameUpdateEventsJs
+from .. import GameContext
+
+router = APIRouter()
+
+
+@router.websocket("/eventstream")
+async def event_stream(websocket: WebSocket) -> None:
+    await websocket.accept()
+    while True:
+        if not (events := await EventStream.get()).empty:
+            await websocket.send_json(
+                jsonable_encoder(
+                    GameUpdateEventsJs.from_events(events, GameContext.get())
+                )
+            )