Allow websocket attributes to be passed to websockets

[ArBridgeman]

Summary

In updating our documentation, it was noticed that some old ODBC parameters had been included. These were removed, but for websocket, we could modify:
https://github.com/exasol/sqlalchemy-exasol/blob/master/sqlalchemy_exasol/websocket.py#L84
so that the attributes go from PyExasol > websocket

https://github.com/exasol/websocket-api/blob/master/docs%2FWebsocketAPIV5.md#attributes-session-and-database-properties