[Type 3] Don't let signin requests be sent if they use http when server expects https #1091

We very often see users getting an inexplicable error because they entered a http url and the server expected https: 405 Method Not Allowed (https://tableau.github.io/server-client-python/docs/sign-in-out#405000-method-not-allowed-response)

Instead, the client library should ping the unauthenticated endpoint and check if ssl is enabled first, and then switch to ssl if supported before sending the initiating request. Don’t even allow someone to send http if https is enabled. (I think Tableau Desktop already does that)