Add ENV variable to debug zeitwerk

It's far easier to debug in dev/test/containers using an ENV variable
so we'll make it so zeitwerk stdout logging and eager loading of all engines
is only done with this flag enabled.

config/application.rb

@@ -164,9 +164,11 @@ class Application < Rails::Application
     end
 
     initializer :eager_load_all_the_things, :after => :load_config_initializers do
-      config.eager_load_paths += config.autoload_paths
-      Vmdb::Plugins.each do |plugin|
-        plugin.config.eager_load_paths += plugin.config.autoload_paths
+      if ENV['DEBUG_MANAGEIQ_ZEITWERK'].present?
+        config.eager_load_paths += config.autoload_paths
+        Vmdb::Plugins.each do |plugin|
+          plugin.config.eager_load_paths += plugin.config.autoload_paths
+        end
       end
     end
 

config/initializers/zeitwerk.rb

@@ -1,6 +1,8 @@
 if Rails.application.config.autoloader == :zeitwerk && Rails.autoloaders.main
-  Zeitwerk::Loader.default_logger = method(:puts)
-  Rails.autoloaders.main.logger = Logger.new(STDOUT)
+  if ENV['DEBUG_MANAGEIQ_ZEITWERK'].present?
+    Zeitwerk::Loader.default_logger = method(:puts)
+    Rails.autoloaders.main.logger = Logger.new(STDOUT)
+  end
 
   # These specific directories are for code organization, not namespacing:
   Rails.autoloaders.main.collapse(Rails.root.join("lib/manageiq/reporting/charting"))