Collection of app router migration guide tasks

[tordans]

I wanted to keep track on changes, so I will list the things I see missing in the current guide at https://blitzjs.com/docs/usage-next-13#app-directory

Blocker

• Update usage-next-13.mdx: Clarify that the API route need to stay in the pages folder #848
• Update usage-next-13.mdx: BlitzProvider as client component #847
• Update usage-next-13.mdx: Clarify /src/app folder #845
• Explain that Blitz Routes don't work in app directory. Explain how to use the experimental types route feature of NextJS App Router and how to use this with as Route whenever a param has to be added.
  See also https://discord.com/channels/802917734999523368/1161595039043047445
• TODO: Explain how to migrate useParams, useRouter, useSearchParams, see also https://discord.com/channels/802917734999523368/1161571344459239495
• TODO: How to work around that next/head is not available in App directory and Metatags are only available in server components which did not work for me (yet). We are considering moving back to ReactHelmet…
• Update usage-next-13.mdx: Still use authConfig #844
• Double check the docs on authentication. All calls like FooPage.authenticate = true need to be replaces with useAuthenticatedBlitzContext. But first there is App Router: useAuthenticatedBlitzContext with redirectAuthenticatedTo results in infinite loop blitz#4246 to be resolved.

Improvements

• Docs usage-next-13.mdx: Add section on the new Metadata and reference invoke #851
• Update usage-next-13.mdx: Hint at loading.tsx files #846
• Update usage-next-13.mdx: Clarify /src/app folder #845

Minor

• (docs) Fix misspell #840
• Update usage-next-13.mdx: remove ".js" file ending #843 => Update usage-next-13.mdx: Still use authConfig #844

[siddhsuresh]

Thanks @tordans this is perfect. I will work on reviewing these and also implement the suggestions in the upcoming template using the app directory