[nuxt] Add `postcss-preset-env` by default to nuxt
enhancement🍰 p2-nice-to-have
# [nuxt] Add `postcss-preset-env` by default to nuxt
Deprecate external `postcss.config` for webpack
enhancement3.x🍰 p2-nice-to-have⚠️ breaking change
PostCSS Preset Env not being loaded by default
stalepending triage2.x