feat(login): use new IDP templates (#5315)

The login uses the new template based IDPs with backwards compatibility for old IDPs

internal/domain/idp.go

@@ -34,3 +34,12 @@ const (
 	IDPTypeGitLabSelfHosted
 	IDPTypeGoogle
 )
+
+func (t IDPType) GetCSSClass() string {
+	switch t { //nolint:exhaustive
+	case IDPTypeGoogle:
+		return "google"
+	default:
+		return ""
+	}
+}