Drop support of webpack-dev-server ^4.8, add support for webpack-dev-server ^5.0

[Kocal]

Close #1290

Upgrade webpack-dev-server didn't have impact for Encore itself, but it can be the case for end-users.

After upgrading webpack-dev-server to ^5.0, my project that use the following devServer configuration is still working as expected:

Encore.configureDevServerOptions((options) => {
    options.allowedHosts = 'all';
    options.client = {
        overlay: false, // hidden overlay: multiple errors caused by third-party scripts
    };
    options.server = {
        type: 'https',
        options: {
            pfx: path.join(process.env.HOME, '.symfony5/certs/default.p12'),
        },
    };
})

[stof]

I suggest mentioning that the supported option in the configuration callback have changed, with a link to their changelog. They have BC breaks in their configuration.

[Kocal]

Done