feat: allow user to modify generated webpack config

lib/webpack/utils.js

@@ -0,0 +1,28 @@
+const merge = require('webpack-merge');
+
+// Modify the generated webpack config with normal webpack config
+function applyConfigureWebpack(userConfig, config, isServer) {
+  if (typeof userConfig === 'object') {
+    return merge(config, userConfig);
+  }
+  if (typeof userConfig === 'function') {
+    const res = userConfig(config, isServer);
+    if (res && typeof res === 'object') {
+      return merge(config, res);
+    }
+  }
+  return config;
+}
+
+// Modify the generated webpack config with webpack-chain API
+function applyChainWebpack(userChainWebpack, config, isServer) {
+  if (userChainWebpack) {
+    userChainWebpack(config, isServer);
+  }
+  
+}
+
+module.exports = {
+  applyConfigureWebpack,
+  applyChainWebpack
+};