Test: Add unit tests for SteamChatBot

Add unit tests for the SteamChatBot module. These tests are designed to
validate the SteamChatBot.Connect() method for three use cases: the user
provides a username and password and no sentry file exists; the user
provides a username, password, and Steam Guard code and no sentry file
exists; and the user provides a username and password and a sentry file
exists.