[Question] How to get payload on connect in aiohttp

simple example:
```python
from graphql_ws.aiohttp import AiohttpSubscriptionServer
from .schema import schema

subscription_server = AiohttpSubscriptionServer(schema)

async def subscriptions(request):
ws = web.WebSocketResponse(protocols=('graphql-ws',))
await ws.prepare(request)
# payload = request.get('payload') ???
await subscription_server.handle(ws, request_context=payload)
return ws

app = web.Application()
app.router.add_get('/subscriptions', subscriptions)

web.run_app(app, port=8000)
```

How to get payload when init connection to socket?
```
{"type":"connection_init","payload":{"FOO":"BAR"}}
```