include postcss-import for proper tailwind support

Created by: kitsunekyo

Is your proposal related to a problem?

a very common use-case of tailwind is using it with the postcss-import plugin https://tailwindcss.com/docs/using-with-preprocessors#build-time-imports

as CRA already provides support for tailwind out of the box and is opinionated about the plugins (flexbugs fixes, preset-env, ...) supporting this use case would be helpful.

Describe the solution you'd like

add postcss-import as a dependency + plugin, to provide proper support for common tailwind features.

Describe alternatives you've considered

• added a postcss.config.js to overwrite the loaderOptions, but the file is just ignored.
  https://github.com/tailwindlabs/tailwindcss/discussions/7049#discussioncomment-1966402
• i've tried craco -> doesn't support CRA5, and I also tried ejecting (which works, but we're trying not to eject any longer)

Additional context

the issue with not having postcss-import available isn't immediately obivious. but it breaks the load order of css imports. https://github.com/tailwindlabs/tailwindcss/issues/7051