Streaming (websockets) support

[Olen]

Just throwing this out here as a start.

I had a quick look at fixing the websockets (streaming) connection to add keepalives etc.
But now I actually don't think it has worked at all since switching to httpx, as httpx does not have WS support...

Traceback (most recent call last):
  File "/usr/local/lib/python3.9/site-packages/teslajsonpy/connection.py", line 288, in websocket_connect
    self.websocket = await self.websession.ws_connect(self.websocket_url)
AttributeError: 'AsyncClient' object has no attribute 'ws_connect'

From this line:

I tried to just replace it with webockets.connect. but that seems to not be a drop in replacement, so it needs a bit more massage before it is usable...

There is a potential problem, that the streaming API seems to only support one client at a time:
teslamate-org/teslamate#753 (comment)

So enabling the streaming API here might interfere with the app. Need to think a bit how to handle that...

[alandtse]

Oh yah, I forgot that the httpx merge would require another websocket library or wait for official support.