[Feature Request] How about add postcssRegex in webpack config?

Created by: SoYoung210

Is your proposal related to a problem?

(Write your answer here.) Yes. When i want to use postcss(pcss), i have to override it.

const cssRule = oneOfRule.oneOf.find(rule => rule.test && rule.test.toString().includes('css'));
cssRule.test = /\.p?css$/;

How about add postcssRegex? (like sass and sassModule)

Describe the solution you'd like

packages/react-scripts/config/webpack.config.js

// style files regexes
const cssRegex = /\.css$/;
const cssModuleRegex = /\.module\.css$/;
const sassRegex = /\.(scss|sass)$/;
const sassModuleRegex = /\.module\.(scss|sass)$/;
const postcssRegex = /\.p?css$/;

...
{
  test: postcssRegex,
  use: getStyleLoaders(
    {
      importLoaders: 2,
      sourceMap: isEnvProduction && shouldUseSourceMap,
      modules: true,
    },
    'postcss-loader'
  )
},

Describe alternatives you've considered

Each user override config.. may be with eject.

Additional context

(Write your answer here.)