## Is your feature request related to a problem?

A user mentioned needing a feature to clone dashboards as they create the same dashboard multiple times, each for a different end-customer. Given that we are already planning on doing default / custom dashboards (#1659) we can add this functionality to facilitate dashboard creation.

## Describe the solution you'd like

Simple functionality to duplicate a dashboard.
- Add "Duplicate" button to dashboard list and clone dashboard (e.g. "Copy - AARRR").
![screenshot](https://user-images.githubusercontent.com/5864173/93866745-fce46100-fcbf-11ea-8c96-b1acfb1981d5.png)


## Describe alternatives you've considered
Re-create the dashboard manually.


## Additional context
No additional context.


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

posthog/api/dashboard.py
queryset = DashboardItem.objects.all()
    serializer_class = DashboardItemSerializer
    permission_classes = [IsAuthenticated, ProjectMembershipNecessaryPermissions, TeamMemberAccessPermission]
    def get_queryset(self) -> QuerySet:
        queryset = super().get_queryset()
        if self.action == "list":
            queryset = queryset.filter(deleted=False)
            queryset = self._filter_request(self.request, queryset)
        order = self.request.GET.get("order", None)
        if order:
            queryset = queryset.order_by(order)
        else:
            queryset = queryset.order_by("order")
        return queryset
    def get_permissions(self):