Introduce Next.js 14 template

[davekiss]

What kind of change does this pull request introduce?

Next.js 14 uses a different routing structure, so I'm introducing that as a new template.

However, I'm seeing an error with the Node version after running yarn dev:react in the project's root to spin up the Storybook:

Seems like the same issue as mentioned here: https://github.com/codesandbox/sandpack/issues/1147

Please let me know what else you might need to get this merged.

Checklist

• [ ] Documentation;
• [x] Storybook (if applicable);
• [ ] Tests;
• [ ] Ready to be merged;