Support dev server public option

[rossta]

This PR allows makes the webpack-dev-server public option configurable through webpacker.yml.

We currently use dnsmasq + nginx to reverse proxy requests from a custom local domain, i.e., myapp.dev, to our local Rails server for development. The recent addition of the DevServerProxy makes it easier for us to configure our setup for serving "packs" (thanks!). However, we'd still like the ability to proxy the dev server auto-refresh websocket connection, i.e., the /sockjs-node endpoint, through nginx as well.

To accomplish this (unless I'm missing an alternative), we would set the dev server public option to our local domain myapp.dev; however, the public is currently assumed to be "#{HOSTNAME}:#{PORT}" in the bin/webpack-dev-server wrapper. These changes ensure that a public option given in webpacker.yml or on the command line are passed through to the webpack-dev-server executable.

I could add a section in docs/webpack-dev-server.md if that would be helpful for documentation.

[p0wl]

nice! needed this just yesterday and wrote a workaround. Would love to see this merged!

In our setup, rails runs in docker but the webpack-dev-server runs on the local machine (because file changes get picked up way faster), so the rails server needs to know the the ip of the webpack-dev-server, but the public option needs to be localhost:3035.

[gauravtiwari]

Thanks @rossta for this but we are thinking to move away from ARGV support for webpack-dev-server and instead provide env variables to achieve same behaviour. The config options currently are spread across - cli args, env and webpacker.yml, which makes it harder to reason. Please see this PR: #793 for more details but I am working on another one, which covers your needs as well :)

[rossta]

@gauravtiwari Thanks for the background. Does that mean this PR pre-empted by yours or should I reimplement based on that work after it's merged?

[gauravtiwari]

@rossta Yepp, the PR will cover your change here :)

[gauravtiwari]

Closing in favour of #843