Add support for third party auth and add Slack OIDC provider

[jan-tennert]

What kind of change does this PR introduce?

Feature

What is the current behavior?

No support for third party auth and missing the Slack OIDC provider.

What is the new behavior?

The provider has been added and there is a new option in the SupabaseClientBuilder:

val supabase = createSupabaseClient(supabaseUrl, supabaseKey) {
    accessToken = {
          //fetch the third party token
         "my-token"
    }
}

If this property is not null, the Auth plugin will not be available and this custom provider function will be used for auth.

Additional context

Check supabase/supabase-js#1004.

[jan-tennert]

Should this also apply to realtime? @grdsdev @dshukertjr

[dshukertjr]

Sorry for the delay, but yes this should work with all services including realtime! Thanks for working on this!