feat(tile): add important highlight variant

[tomdavies73]

Proposed behaviour

Changes the highlight variants to better fit the Tile and align with DS designs (small, default and large roundness pictured)

Adds the "important" variant which is available via the highlightVariant prop

Current behaviour

Currently, there is no "important" variant available via the highlightVariant prop and the highlight variants available on Tile are not aligned with the design system.

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