websocket auth check and updates to docs referencing kwargs for keys, base_url

[bdowling]

I thought it might be useful to have the ability to independently set the polygon API key_id. In the current environment, this can be useful if a funded account holder wants to use the paper trading API with polygon (paper keys do not currently work with polygon NATs).

Also updated the readme to provide a little more clarity on passing this and the other keys to the API.

Note: this PR also adds a bit of checking for the websocket API credential check, raising an error if it is not successful. This does not address the polygon auth errors.

[umitanuki]

Paper-only account does not work with polygon, but paper account for the user who has live account should work with polygon.

[umitanuki]

This change would break existing uses, since most of the users have no problem with Alpaca key id for polygon.

[bdowling]

@umitanuki I tried to make it as backwards compatible as possible, the POLYGON key ID is optional, it will default to using the provided APAC_API_KEY_ID, providing preference to the kwarg, environment, then default.

[bdowling]

Actually, now that I looked back at this, I think I fixed a non-issue. The Alpaca side websocket streaming API is unavailable to paper trading credentials. I came back to this thinking the NATs was having the issue with paper trading keys (my tokens had reset).

It does provide the error message now though to let you know (otherwise it's just hidden in the authorization stream if you don't specify a handler for that).

ValueError: Invalid Alpaca API credentials, Failed to authenticate: {'stream': 'authorization', 'data': {'action': 'authenticate', 'status': 'unauthorized'}}