feat: Modelling per group type + group overview pages

[timgl]

Problem

The way our current modelling works is confusin for customers. This PR massively simplifies it by putting the modelling onto the groups itself (will do persons separately).

Also adds an overview dashboard to groups.

All behind cs-dashboards feature flag.

Changes

👉 Stay up-to-date with PostHog coding conventions for a smoother review.

Does this work well for both Cloud and self-hosted?

How did you test this code?

[Gilbert09]

@timgl Seems like there's a bunch of random file adds/edits in here too

[github-actions]

Size Change: +63 B (+0.01%)

Total Size: 1.12 MB

ℹ️ View Unchanged

Filename	Size	Change
frontend/dist/toolbar.js	1.12 MB	+63 B (+0.01%)

_{compressed-size-action}

[posthog-bot]

This PR hasn't seen activity in a week! Should it be merged, closed, or further worked on? If you want to keep it open, post a comment or remove the stale label – otherwise this will be closed in another week. If you want to permanentely keep it open, use the waiting label.

[posthog-bot]

This PR was closed due to lack of activity. Feel free to reopen if it's still relevant.