Currently, Mongoid has a generator which generates `config/mongoid.yml` for new apps.

In addition, for Rails apps, we should generate `config/initializers/mongoid.rb`. This important after releasing MONGOID-5293 (config.load_defaults option), to ensure all newly generated apps are properly locking their Mongoid version.

The generated initializer should look like:

# config/initializers/mongoid.rb

Mongoid.configure do

  # Load Mongoid behavior defaults. This automatically sets
  # features flags (refer to documentation)
  config.load_defaults[<%= Mongoid::VERSION %>]
end

# Enable Mongo driver query cache for Rack
# Rails.application.config.middleware.use(Mongo::QueryCache::Middleware)

# Enable Mongo driver query cache for ActiveJob
# ActiveSupport.on_load(:active_job) do
#   include Mongo::QueryCache::Middleware::ActiveJob
# end

I've included the latter two Query cache items because users should be aware of these. They should probably be commented out by default.