Nuage provider assumes Qpid constant is loaded or autoloadable

manageiq-providers-nuage can be eager loaded on all platforms.  It's dependency,
qpid_proton, is hidden because it can't be required on macos. Because this is an
optional dependency, any platforms that can install it will need to eager require it
since EventCatcher::MessagingHandler needs it at require/load time.

The alternative is to make qpid_proton require work on mac and define these constants.

For example:
class ManageIQ::Providers::Nuage::NetworkManager::EventCatcher::MessagingHandler < Qpid::Proton::MessagingHandler
...
end
https://github.com/ManageIQ/manageiq-providers-nuage/blob/541494cded64b1ef281c71767d7d5f88cf4bb08d/app/models/manageiq/providers/nuage/network_manager/event_catcher/messaging_handler.rb#L1

Gemfile

@@ -189,7 +189,11 @@ group :red_hat_virtualization, :manageiq_default do
 end
 
 group :qpid_proton, :optional => true do
-  gem "qpid_proton",                    "~>0.30.0",          :require => false
+  # We're eager requiring the qpid_proton gem on platforms that install it because
+  # zeitwerk wants to be able to eager/autoload the nuage provider which expects
+  # qpid constants to be defined.  For mac platform, we have stubs for these constants
+  # defined in lib/qpid/proton.
+  gem "qpid_proton",                    "~>0.30.0"
 end
 
 group :systemd, :optional => true do