## Bug description

When going to instance status > internal metrics and refreshing the dashboard, the loading fails

https://user-images.githubusercontent.com/148820/120655500-693c7480-c48b-11eb-8c75-6afd4c967506.mp4

## Expected behavior

It reloads successfully

## How to reproduce

See above

## Environment

- [x] PostHog Cloud
- [x] self-hosted PostHog, version/commit: latest

## Additional context

Seems the cause is that "refresh" requests data from `/api/insight/trends` vs getting it from `/api/dashboard/id` as on first load.

Relates to #3609  

#### *Thank you* for your bug report – we love squashing them!

posthog/api/dashboard.py
items = serializers.SerializerMethodField()
    created_by = UserBasicSerializer(read_only=True)
    use_template = serializers.CharField(write_only=True, allow_blank=True, required=False)
    class Meta:
        model = Dashboard
        fields = [
            "id",
            "name",
            "description",
            "pinned",
            "items",
            "created_at",
            "created_by",
            "is_shared",
            "share_token",
            "deleted",
            "creation_mode",
            "use_template",
            "filters",
            "tags",
        ]
        read_only_fields = ("creation_mode",)
    def create(self, validated_data: Dict, *args: Any, **kwargs: Any) -> Dashboard: