Can't get querystring parameters on connect

Hey guys,

Would be incredible to have querystring parameters in the event.

```
class WebsocketEvent(BaseLambdaEvent):
def __init__(self, event_dict: Dict[str, Any], context: Any):
super(WebsocketEvent, self).__init__(event_dict, context)
self._json_body: Optional[Dict[str, Any]] = None

def _extract_attributes(self, event_dict: Dict[str, Any]) -> None:
request_context = event_dict['requestContext']
self.domain_name: str = request_context['domainName']
self.stage: str = request_context['stage']
self.connection_id: str = request_context['connectionId']
self.body: str = str(event_dict.get('body'))
self.query_params: str = str(event_dict.get('queryStringParameters')) # <------------- I'm using like that.
```
...

Start with WebsocketEvent._extract_attributes and the event_dict queryStringParameters entry shown in the issue. Trace how WebsocketEvent exposes event fields, then make the connection event's query-string parameters available there and verify that the resulting event includes them.

Written by the indexing model from the issue text.