Add webpack-encore for symfony project

.gitignore

assets/app.js

assets/bootstrap.js

assets/controllers.json

assets/controllers/hello_controller.js

assets/styles/app.scss

composer.lock

config/bundles.php

config/packages/assets.yaml

config/packages/prod/webpack_encore.yaml

config/packages/test/webpack_encore.yaml

config/packages/webpack_encore.yaml

package-lock.json

package.json

postcss.config.js

symfony.lock

webpack.config.js