test(sidebar): move pw tests to storybook interaction

[paulrobinson88]

Proposed behaviour

• Removes flaky tests from the playwright file for sidebar component.
• Adds one interaction test to cover the removed Playwright scenarios.
• Removes references to Cypress testing from select and draggable.
• Updates testing-guide and readme file to remove inaccuracies.

Current behaviour

• There are 4 flaky skipped tests in the Playwright file for the sidebar component
• Some component docs make reference to Cypress which is no longer part of the repo.
• The testing-guide and readme file have some incorrect information.

Checklist

• Commits follow our style guide
• Related issues linked in commit messages if required
• Screenshots are included in the PR if useful
• All themes are supported if required
• Unit tests added or updated if required
• Playwright automation tests added or updated if required
• Storybook added or updated if required
• Translations added or updated (including creating or amending translation keys table in storybook) if required
• Typescript d.ts file added or updated if required
• Related docs have been updated if required

QA

• Tested in provided StackBlitz sandbox/Storybook
• Add new Playwright test coverage if required
• Carbon implementation matches Design System/designs
• UI Tests GitHub check reviewed if required

Additional context

Testing instructions