Share project dashboard to org members without project permissions

[aspicer]

Feature request

From here: https://posthoghelp.zendesk.com/agent/tickets/18142

A customer wants to be able to share dashboards to org users only (and embed these dashboards in iframes, but behind a login), but not give those users permission to the specific project the dashboard comes from.

Debug info

- [ ] PostHog Cloud, Debug information: [please copy/paste from https://us.posthog.com/settings/project-details#variables]
- [ ] PostHog Hobby self-hosted with `docker compose`, version/commit: [please provide]
- [ ] PostHog self-hosted with Kubernetes (deprecated, see [`Sunsetting Kubernetes support`](https://posthog.com/blog/sunsetting-helm-support-posthog)), version/commit: [please provide]