Move eager load before forking process for Prometheus

lib/prometheus/controller.rb

@@ -12,6 +12,7 @@ module Prometheus
       def initialize_metrics
         register_metrics
 
+        Rails.application.eager_load!
         Thread.new do
           initialize_instance_count
           initialize_rfc_metrics
@@ -33,7 +34,6 @@ module Prometheus
       end
 
       def initialize_instance_count
-        Rails.application.eager_load!
         ApplicationRecord.descendants.reject(&:abstract_class).each do |each|
           @instance_count.observe(each.count, class: each.name)
         end