Set dev server listen host and port via environment variables

[monai]

Resolve #767.

[javan]

If we're going to support ENV vars, I think we should convert all of bin/webpack-dev-servers ARGVs to them.

[javan]

These should all match their method names, e.g. ENV["WEBPACK_DEV_SERVER_HOST"]

[gauravtiwari]

Yepp and may be best to get rid of ARGV support for dev server binstub and add important ones to webpacker.yml itself? Obviously for run time options (host etc.) we can have ENV variables.

[javan]

Yeah, I'd like to drop ARGV support in favor of ENV. Maybe like this?

--- a/lib/webpacker/dev_server.rb
+++ b/lib/webpacker/dev_server.rb
@@ -42,7 +42,7 @@ class Webpacker::DevServer
 
   private
     def fetch(key)
-      config.dev_server.fetch(key, defaults[key])
+      ENV["WEBPACK_DEV_SERVER_#{key.upcase}"] || config.dev_server.fetch(key, defaults[key])
     end

[gauravtiwari]

Yepp looks great 👍

[monai]

And in binstub we can take all WEBPACK_DEV_SERVER_ variables and merge them with config file. I'm going to update PR in few days.

[gauravtiwari]

@monai This involves a few more changes so I am going to make another PR that covers everything 👍

[gauravtiwari]

Closing in favour of #843