## Is your feature request related to a problem?

When setting up dashboards I'd like to filter the stats to a certain page/subdomain. 

## Describe the solution you'd like

Allow adding a extra filters for all graphs on a dashboard (e.g. filter by $current_url)

## Describe alternatives you've considered

Updating every graph in dashboard one-by-one and then reverting them back.

## Additional context

Related to https://github.com/PostHog/posthog/issues/780

Datadog has a decent solution for this: https://docs.datadoghq.com/dashboards/template_variables/, which I think we can simplify and use ourselves.

Came up during #2560 

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

posthog/api/dashboard.py
return dashboard.get_effective_privilege_level(self.context["request"].user.id)
    def validate(self, data):
        if data.get("use_dashboard", None) and data.get("use_template", None):
            raise serializers.ValidationError("`use_dashboard` and `use_template` cannot be used together")
        return data
    def _update_creation_mode(self, validated_data, use_template: str, use_dashboard: int):
        if use_template:
            return {**validated_data, "creation_mode": "template"}
        if use_dashboard:
            return {**validated_data, "creation_mode": "duplicate"}
        return {**validated_data, "creation_mode": "default"}
class DashboardsViewSet(TaggedItemViewSetMixin, StructuredViewSetMixin, viewsets.ModelViewSet):
    queryset = Dashboard.objects.order_by("name")
    serializer_class = DashboardSerializer
    authentication_classes = [
        PersonalAPIKeyAuthentication,
        SessionAuthentication,
        BasicAuthentication,
    ]
    permission_classes = [
        IsAuthenticated,
        ProjectMembershipNecessaryPermissions,
        TeamMemberAccessPermission,
        CanEditDashboard,
    ]
    def get_queryset(self) -> QuerySet: