## Is your feature request related to a problem?

Currently if you login with SAML and you don't have an account on the PostHog instance one of two things happen: a) either a new account is created **if the email matches the domain whitelist** or b) you get turned down at the door. Yet after some thought, the point of SAML is that you manage user provisioning in a separate centralized system, so we shouldn't have the extra domain check. 

## Describe the solution you'd like

If a user logins through SAML and their account doesn't exist, create it automatically, regardless of whether it matches the domain whitelist.


## Describe alternatives you've considered

Keeping as is.

## Additional context

There's a complicating factor which is that SAML login is instance-based yet user signup is organization-based, so there's the edge case of an instance having multiple orgs. Should the user then be signed up to all organizations?

#### *Thank you* for your feature request – we love each and every one!

posthog/api/signup.py
if self.enable_new_onboarding(user):
            return create_demo_team(organization=organization)
        else:
            return Team.objects.create_with_data(user=user, organization=organization)
    def to_representation(self, instance) -> Dict:
        data = UserBasicSerializer(instance=instance).data
        data["redirect_url"] = "/personalization" if self.enable_new_onboarding() else "/ingestion"
        return data
    def enable_new_onboarding(self, user: Optional[User] = None) -> bool:
        if user is None:
            user = self._user
        return posthoganalytics.feature_enabled("new-onboarding-2822", user.distinct_id)
class SignupViewset(generics.CreateAPIView):
    serializer_class = SignupSerializer
    
    permission_classes = (permissions.AllowAny,) if settings.E2E_TESTING else (CanCreateOrg,)
class InviteSignupSerializer(serializers.Serializer):
    first_name: serializers.Field = serializers.CharField(max_length=128, required=False)
    password: serializers.Field = serializers.CharField(required=False)
    email_opt_in: serializers.Field = serializers.BooleanField(default=True)
    def validate_password(self, value):