docs: update storefront ui info

[mattmaribojoc]

With the new Storefront UI Launch, some of the links on the docs need to be updated.

Description

This PR updates the Vuepress theme to use the latest links and an image from https://docs.vuestorefront.io/v2/sfui-hero.png (this image will be deployed as a part of this PR)

It also adds some additional config required as part of bumping the theme dependency

Related Issue

Motivation and Context

How Has This Been Tested?

Screenshots:

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [ ] I have read the CONTRIBUTING document.

Changelog

• [ ] I have updated the Changelog (V1) v2 and mentioned all breaking changes in the public API.
• [ ] I have documented all new public APIs and made changes to existing docs mentioning the parts I've changed so they're up to date.

Tests

• [ ] I have written test cases for my code
• [ ] I have tested my Pull Request on production build and (to my knowledge) it works without any issues
• [ ] I have added tests to cover my changes.
• [ ] All new and existing tests passed.

  I tested manually my code, and it works well with both:

• [ ] Default Theme
• [ ] Capybara Theme

Code standards

• [ ] My code follows the code style of this project.
• [ ] I have followed naming conventions

Docs

• [x] My change requires a change to the documentation.
• [x] I have updated the documentation accordingly.