move dev server middleware to new namespace

config/initializers/static_files.rb

@@ -34,7 +34,7 @@ if app.config.serve_static_files
       )
       app.config.middleware.insert_before(
         Gitlab::Middleware::Static,
-        Gitlab::Middleware::WebpackProxy,
+        Gitlab::Webpack::DevServerMiddleware,
         proxy_path: app.config.webpack.public_path,
         proxy_host: dev_server.host,
         proxy_port: dev_server.port

lib/gitlab/webpack/dev_server_middleware.rb

@@ -3,8 +3,8 @@
 
 # :nocov:
 module Gitlab
-  module Middleware
-    class WebpackProxy < Rack::Proxy
+  module Webpack
+    class DevServerMiddleware < Rack::Proxy
       def initialize(app = nil, opts = {})
         @proxy_host = opts.fetch(:proxy_host, 'localhost')
         @proxy_port = opts.fetch(:proxy_port, 3808)