feat(data-exploration): implement trends insight

[thmsobrmlr]

Todos

• [x] Series label
• [x] Formula mode
  • [ ] Error handling for invalid formula e.g. A + B / 100
• [ ] Smoothing
• [ ] Y-axis unit
• [x] Breakdown
• [x] Placeholder

Problem

Changes

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

How did you test this code?

[posthog-bot]

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