## 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/test/test_insight.py
with freeze_time("2012-01-14T03:21:34.000Z"):
            for i in range(25):
                _create_event(
                    team=self.team, event="$pageview", distinct_id="1", properties={"$some_property": f"value{i}"},
                )
        with freeze_time("2012-01-15T04:01:34.000Z"):
            response = self.client.get(
                f"/api/projects/{self.team.id}/insights/trend/",
                data={"events": json.dumps([{"id": "$pageview"}]), "compare": "true",},
            )
        self.assertEqual(response.status_code, status.HTTP_200_OK)
        result = response.json()
        self.assertEqual(len(result["result"]), 2)
        self.assertEqual(result["result"][0]["compare_label"], "current")
        self.assertEqual(result["result"][1]["compare_label"], "previous")
    def test_insight_trends_breakdown_pagination(self):