Wait a few seconds after socket connection for first ping, to prevent…

[bartvanb]

… non-connected namespace error

This prevents this error directly after startup:

2023-03-23 14:18:33 - node           - ERROR    - Ping thread had an exception
Traceback (most recent call last):
  File "/vantage6/vantage6-node/vantage6/node/__init__.py", line 812, in __socket_ping_worker
    self.socketIO.emit('ping', namespace='/tasks')
  File "/usr/local/lib/python3.10/site-packages/socketio/client.py", line 393, in emit
    raise exceptions.BadNamespaceError(
socketio.exceptions.BadNamespaceError: /tasks is not a connected namespace.