chore: Iframe test pages

[pan-kot]

Description

The PR adds test pages to validate this fix: cloudscape-design/components#4005 works.

How has this been tested?

Review checklist

The following items are to be evaluated by the author(s) and the reviewer(s).

Correctness

• Changes include appropriate documentation updates.
• Changes are backward-compatible if not indicated, see CONTRIBUTING.md.
• Changes do not include unsupported browser features, see CONTRIBUTING.md.
• Changes were manually tested for accessibility, see accessibility guidelines.

Security

• If the code handles URLs: all URLs are validated through the checkSafeUrl function.

Testing

• Changes are covered with new/existing unit tests?
• Changes are covered with new/existing integration tests?

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[jperals]

Two questions:

• fix: Fixes chart popover click outside when in iframe components#4005 fixes the chart popover behavior in the components repo. How does that affect these chart components? Or is this rather about being able to spot similar issues in this repo in the future?
• Any plans for test coverage, or just manual testing?

[pan-kot]

Two questions:

• fix: Fixes chart popover click outside when in iframe components#4005 fixes the chart popover behavior in the components repo. How does that affect these chart components? Or is this rather about being able to spot similar issues in this repo in the future?
• Any plans for test coverage, or just manual testing?

1. The issue was in the chart popover, which is imported by chart-components (via internal do-not-use namespace).
2. I don't think we need to cover it here with automation as the actual behaviour is already well tested in the components repo. However, I find that having an iframe testing page is useful as there might be more issues like that discovered in the future.