New insight type - Change Chart

Describe the solution you'd like

A chart that help displays changes in trends over time. Idea has come from: https://github.com/PostHog/posthog/pull/53982

Problem:

Spotting directional trends across breakdown values when there are too many series for a line chart can be useful.

For example, if I have a “movie watched” event broken down by language, a standard line chart gets noisy pretty quickly. What I’m usually trying to answer is: which languages are trending up vs down over a given window? The change-style chart makes that comparison much more obvious at a glance.

The chart was inspired from this very similar chart that I found very helpful to spot trends of this week vs last week.

Seems like a good idea, we should support this or similar.

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]

Start by reviewing the linked PostHog pull request #53982 and the Datadog reference chart to understand the proposed comparison. Done should be a supported change-style chart that makes upward and downward trends across breakdown values clear over a selected time window.