add ObservablePlot component and update ChartContainer

[jamesscottbrown]

What does this change?

This adds a first version of a component to render a chart using ObservablePlot.

It also updates the ChartContainer component.

Why?

How?

Related issues:

Does this introduce new dependencies?

Yes - @observablehq/plot.

How is it tested?

Only using the Storybook stories.

How is it documented?

Are light and dark themes considered?

Is it complete?

• [x] Have you included changeset file?
• [x] If this adds a new component, is it exported via index.js?