Chore: (Tutorials - Visual Testing Handbook) Storybook 7.0 changes

[jonniebigodes]

With this pull request the required 7.0 changes were included for the Visual testing handbook tutorial. What was done:

• Updated assets
• Updated code samples to factor in CSF 3 announced with version 7.0
• Updated commit hashes
• Updated the version in gatsby-config.js to reflect the recent version release