Add a timeseries chart view for metric deltas and credible intervals

[jurajmajerik]

Feature request

Is your feature request related to a problem?

From a customer:

having a time series view of the metric delta + CI's with ability to see the aggregated imapct of a metric for a particular time period (e.g. last 7 days) would be helpful for us to gauge novelty effects and also remove them if needed
Oftentimes you want to exclude data from the first few days when measuring impact

Context: https://github.com/PostHog/product-internal/issues/667#issuecomment-2503355835

Describe the solution you'd like

Describe alternatives you've considered

Additional context

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]