Add authentication provider management

[tommoor]

A new screen under team settings "Authentication" lists the providers connected to the team, it should:

• Allow connecting providers from those available.
• Allow disabling providers that were previously connected (enabled column already exists and defaulted to true for this). Disabled providers should prevent further logins and show an error message on the login screen that explains to the user.
• If attempting to connect a provider already on another team then it can error in a first version

[stale]

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[almereyda]

• Allow adding/merging authentication methods onto one user #2494