refactor: [M3-7449] - Dismissible Banner v7 story migration

[coliu-akamai]

Description 📝

• MIgrated DismissibleBanner component story to a V7 (.tsx) story

Changes 🔄

• migrated story
• added tests
• removed index file + updated exports

How to test 🧪

Prerequisites

• pull code
• yarn && yarn storybook

Verification steps

• checkout http://localhost:6006/?path=/docs/components-notifications-dismissible-banners--documentation + confirm story loads properly
• Confirm no regression for DismissibleBanner on CM
• yarn test DismissibleBanner/DismissibleBanner.test.tsx

As an Author I have considered 🤔

Check all that apply

• 👀 Doing a self review
• ❔ Our contribution guidelines
• 🤏 Splitting feature into small PRs
• ➕ Adding a changeset
• 🧪 Providing/Improving test coverage
• 🔐 Removing all sensitive information from the code and PR description
• 🚩 Using a feature flag to protect the release
• 👣 Providing comprehensive reproduction steps
• 📑 Providing or updating our documentation
• 🕛 Scheduling a pair reviewing session
• 📱 Providing mobile support
• ♿ Providing accessibility support

[tyler-akamai]

Verified:

• http://localhost:6006/?path=/docs/components-notifications-dismissible-banners--documentation + confirm story loads properly
  • Tested the variants
  • Refreshed the page
    
• no regression for DismissibleBanner on CM
• yarn test DismissibleBanner/DismissibleBanner.test.tsx passes

[abailly-akamai]

Nice cleanup and enhanced test! Approving pending fix for StyledLinkButton