Login buttons are constant regardless of available login types

[Alistair Chapman]

When self-hosting Watchparty, the top bar will still always show Email, Facebook and Google sign-in methods, regardless of what providers are actually available on the Firebase end.

For example, in my deployment, I have disabled Facebook and Email, but enabled OIDC to connect with an SSO provider. However, there is no way for a user to actually log in with OIDC, and a non-functional Facebook login is still offered in the UI since TopBar.tsx has the three login methods hard-coded in.

Would it be possible to:

• Have a configuration option (something like REACT_APP_ENABLE_*, or REACT_APP_LOGIN_PROVIDERS) to enable/disable specific login providers
• Add/allow logging in by OIDC, or any of the other Firebase-supported login providers (i.e. GitHub, Microsoft etc)

[Howard Chung]

This is a good idea--I like the idea of having a client side variable to configure it. We do need to add a UI implementation for each supported option though