HMR when using Encore in virtual machine

[louismariegaborit]

Since webpack-dev-server 4.0.0, public option is not available.
The PR #1058 replace public with client-web-socket-url to set url used to generate entry asset in entrypoints.json.

But when we use client-web-socket-url option with a custom domain, url used for the websocket url is wrong. The path /ws is missing and HMR doesn't work.

When I read the webpack-dev-sever documentation for the client-web-socket-url, I think it's not a good idea to use the webpack option client-web-socket-url to set the public url because the format is not the same.

I will send a PR which should solve the problem.