## Bug description

Support refreshing all dashboard items. This feature was temporarily removed because it wasn't working properly)

## Expected behavior
- All dashboard items should be properly refreshed and the `items` object in the `dashboardLogic` should contain the latest information.
- From user feedback. I expect items to be automatically refreshed every hour or so (e.g. if I'm a marketer that looks at graphs continuously during the day, or have a screen dedicated just to metrics).


## How to reproduce

1. Create a dashboard with multiple items
2. Attempt to refresh all and check the last refresh timestamp for each item (remember to uncomment relevant code)

## Environment

- [X] PostHog Cloud
- [X] self-hosted PostHog, version/commit: _please provide_

## Additional context
Follow-up to #3363

## Technical context

When refreshing all dashboard items (via `refreshAllDashboardItems()`) not all items are consistently refreshed all the time. Tested for instance with a dashboard with a couple of mixed (different type) graphs. Some items are still kept on "last refreshed 10 minutes ago".

In addition to the above, as originally reported on #3608, when calling `refreshAllDashboardItems` we update each item in their own scope, which means that the general `items` object in the upper scope logic (`dashboardLogic.js`) doesn't get updated. Not sure if we should propagate the change upwards, re-fetch everything, or just do a general refresh.

The UX problem this is causing is that the "Last refreshed" label now introduced in the dashboards gets outdated because `items` doesn't get updated. Having this object with outdated information also leads to other confusing UX issues.


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

posthog/api/dashboard.py
import secrets
from typing import Any, Dict, Optional
import posthoganalytics
from django.db.models import Model, Prefetch, QuerySet
from django.db.models.query_utils import Q
from django.http import HttpRequest
from django.shortcuts import get_object_or_404
from django.utils.timezone import now
from django.views.decorators.clickjacking import xframe_options_exempt
from rest_framework import authentication, response, serializers, viewsets
from rest_framework.decorators import action
from rest_framework.exceptions import AuthenticationFailed, NotFound
from rest_framework.permissions import IsAuthenticated
from rest_framework.request import Request
from posthog.api.routing import StructuredViewSetMixin
from posthog.api.shared import UserBasicSerializer
from posthog.auth import PersonalAPIKeyAuthentication, PublicTokenAuthentication
from posthog.helpers import create_dashboard_from_template
from posthog.models import Dashboard, DashboardItem, Team
from posthog.permissions import ProjectMembershipNecessaryPermissions
from posthog.utils import get_safe_cache, render_template, str_to_bool
class DashboardSerializer(serializers.ModelSerializer):