KT-72838: [Gradle] Support websockets in webpack devServer proxy

[broundee]

Fixes KT-72838

Add ws parameter to webpack devServer proxy DSL in gradle plugin so that it is passed through to the generated webpack config.

The parameter is not listed in the webpack docs, but it's described in the underlying library's docs here:

option.ws: true/false: if you want to proxy websockets

[JSMonk]

@broundee Thank you so much for the contribution 🙏