feat(plugin-webpack): support for dev server custom headers (#3653)

Co-authored-by: Kevin Cui <[email protected]>

packages/plugin/webpack/src/WebpackPlugin.ts

@@ -554,6 +554,7 @@ the generated files). Instead, it is ${JSON.stringify(pj.main)}`);
       setupExitSignals: true,
       static: path.resolve(this.baseDir, 'renderer'),
       headers: {
+        ...this.config.devServer?.headers,
         'Content-Security-Policy': cspDirectives,
       },
     };