Update Packages - Githubissues

This will be the last update using Next.js Pages router.

This PR updates the packages and fixes some small file exports and references. The next PR TODO: ADD LINK HERE will change from the Pages router to the App Router.

Using next/iamges
Update and use correct Eslint extensions
Fix tailwind warning (update to 3.x)
Add assets.tina.io to allowed remotePatterns
Add support for nested posts
Removes unused files
Update Vercel pipeline to use node v18 + update GitHub workflows to use node18
Packages updated:
- @types/node: ^16.11.7 -> ^20.14.4
- @types/react: ^17.0.35 -> ^18.3.3
- @typescript-eslint/eslint-plugin: ^5.20.0 -> ^7.13.1
- @typescript-eslint/parser: ^5.20.0 -> ^7.13.1
- eslint: ^8.13.0 -> ^9.5.0
- postcss-import: ^14.0.2 -> ^16.1.0
- postcss-nesting: ^10.1.0 -> ^12.1.5
- @headlessui/react: 1.7.5 -> 1.7.19
- date-fns: ^2.23.0 -> ^3.6.0
- next: ^13.3.1 -> ^14.2.4
- react-icons: ^4.2.0 -> ^5.2.1
- tinacms: ^1.5.24 -> ^1.6.4
- typescript: ^4.5.2 -> ^5.4.5

tinacms / tina-cloud-starter

Update Packages #510

This will be the last update using Next.js Pages router.