[webpack-dev-server] Deprecated `onBeforeSetupMiddleware`

[Arthurk12]

Description

Currently when running npm start in a plugin built using this template, the below warning is prompted:

(node:7082) [DEP_WEBPACK_DEV_SERVER_ON_BEFORE_SETUP_MIDDLEWARE] DeprecationWarning: 'onBeforeSetupMiddleware' option is deprecated. Please use the 'setupMiddlewares' option.
(Use `node --trace-deprecation ...` to show where the warning was created)

It seems like the webpack hook onBeforeSetupMiddleware has been deprecated in webpack-dev-server. The recomendation is to use setupMiddlewares instead.

• feat: add setupMiddlewares option webpack/webpack-dev-server#4068
• https://webpack.js.org/configuration/dev-server/#devserversetupmiddlewares