fix: Use standard PostCSS configuration in create-next-app format for ecosystem compatibility (part 2)

[ndelangen]

What?

See #77376 by @kasperpeulen

This PR continues what was done there, converting the remainning template postcss config files to the standard format.

Why?

The array string format for PostCSS plugins is non-standard, and gives errors when loading using postcss-load-config:

TypeError: Invalid PostCSS Plugin found at: plugins[0]
This change ensures that Next.js applications using Tailwind CSS can seamlessly integrate with these tools without requiring manual configuration fixes. For example, vitest will crash, which uses postcss-load-config under the hood:
storybookjs/storybook#30878

How?

Modified the PostCSS configuration in both JavaScript and TypeScript empty app templates with Tailwind to use the object-based plugin format, which is the standard format recognized by PostCSS tools in the ecosystem.

Array syntax:

const config = {
  plugins: ["@tailwindcss/postcss"],
};

export default config;

Object syntax

 const config = {
  plugins: {
    "@tailwindcss/postcss": {},
  },
};

[ijjk]

Allow CI Workflow Run

• approve CI run for commit: 9470d0d

Note: this should only be enabled once the PR is ready to go and can only be enabled by a maintainer

[stefanprobst]

cf #79949

[stefanprobst]

@ndelangen #79949 has been merged so i think this one can be closed.