Issue #3414395: Drush 12 compatibility

I didn't:

• moved rabbitmq.commands declaration from drush.services.yml to rabbitmq.services.yml
• deleted drush.services.yml

It is still working with Drush 10/11 as it is. Drush 12 is able to auto-detect the command since it is now located in the correct directory.

When we will want to drop Drush 10/11 support, we just will have to delete drush.services.yml