Fix webpack errors due to host header check
gitlab!46459 (merged) enables webpack host header checks.
DEV_SERVER_HOST
needs to match the host we use to connect to the
webpack dev server. We use webpack
to connect to the server from Rails for proxying.
We also specify the public address so that it isadded to the allowed hosts since the websocket for livereload connects directly to this address.
Edited by Heinrich Lee Yu