Add new metric trend visualization

What does this MR do and why?

PoC MR to add a new fit for purpose "metric trend" visualization to shared analytics dashboards:

• adds a new metric visualization
• adds related stories

Follow-ups:

• Follow-up MR to provide dashboard wrapper in storybook - !159316 (merged)
• Follow-up MR to test on AI Impact + resolve outstanding questions - !165457 (closed)

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

With trend	Flat trend

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.