module.exports = {
    //...
    output: {
        path: path.resolve(__dirname, '../backend/frontend')
    }
};

module.exports = {
    //...
    plugins: [
        new FileManagerPlugin({
            onEnd: [{
                copy: [
                    {
                        source: path.join(__dirname, 'dist'),
                        destination: path.join(__dirname, '../backend/frontend')
                    }
                ]
            }]
        })
    ]
};