Support Auth0 for User Login

[dylanpomeroy]

Currently the app only supports login for users via Google OAuth2. For greater use in organizations that do not use Google extensively for employee authentication, this is limiting. Building support for setting up Askaway that supports Auth0 login would let the app take advantage of all the social logins included with Auth0, including Microsoft Teams, GitHub, LinkedIn etc. (including Google).

In order to not rely on a single service, we should allow a config option to switch between the two authentication methods. The 3rd party to use can be left to the person configuring Askaway for what best suits their organization.