How to build an Angular library with a separate Webpack.config?

Question

Angular

I created the Angular library inside the workspace itself.
How to tell angular that it needs to be built not through angular.json but through its own webpack.config?
Now the angular.json configurator is like this:

"test-lib": {
      "projectType": "library",
      "root": "projects/test-lib",
      "sourceRoot": "projects/test-lib/src",
      "prefix": "tl",
      "architect": {
        "build": {
          "builder": "@angular-devkit/build-ng-packagr:build",
          "options": {
            "tsConfig": "projects/test-lib/tsconfig.lib.json",
            "project": "projects/test-lib/ng-package.json"
          }
        }
}

And my custom webpack is:

var path = require("path");
var webpack = require("webpack");

module.exports = {
  module: {
    rules: [
      {
        test: /\.css$/,
        include: path.join(__dirname, './projects/src/lib'),
        use: [
          'style-loader',
          {
            loader: 'typings-for-css-modules-loader',
            options: {
              modules: true,
              namedExport: true
            }
          }
        ]
      },
        {
            test: /\.scss$/,
            exclude: /node_modules/,
            use: [
                "style-loader",
                {
                    loader: "typings-for-css-modules-loader",
                    options: {
                        modules: true,
                        namedExport: true,
                        silent: true,
                        localIdentName: production ? "r_[hash:base64:5]" : "[local]___[hash:base64:5]"
                    }
                },
                { loader: "sass-loader" }
            ]
        }
    ]
},

  plugins: [
    new webpack.DefinePlugin({
      'STABLE_FEATURE': JSON.stringify(true),
      'EXPERIMENTAL_FEATURE': JSON.stringify(false)
    })
  ]
};

The library is built by the command: ng build test-lib