Add additional builtin options for authentication

[chand1012]

Rather than only offering the current two authentication methods, organizations will want as many options for authentication as possible. For now we only support GitHub and Discord, and one limitation of that is that both show up in the list even if they're disabled. We should set up the following:

• If an authentication method is disabled, hide it
• If an auth method is enabled, show it
• Support as many auth methods as possible. Should be possible to support anything that NextAuth supports.
• Add email as an option if an organization doesn't want SSO.

There will have to be standard names for each secret and access key for each auth provider. This will be an ongoing project, and will probably end up being an "add it on demand" feature.