Use `@clerk/testing` package to generate and use testing tokens

[anagstef]

This PR:

• Updates Next.Js to 14.2
• Updates Cypress to 13.9
• Updates Clerk to Core 2 + clerkMiddleware
• Uses the @clerk/testing package for Testing Tokens
• Convert the whole repo to Typescript
• Removes unnecessary next static files

[anagstef]

This is blocked due to an investigation going on about how the Clerk behaves in iframes.