Merge branch 'backport_setting_prometheus_metrics_env' into 'master'

set ENV['prometheus_multiproc_dir'] in config/boot.rb instead of config.ru

See merge request !2151

config.ru

@@ -15,9 +15,6 @@ if defined?(Unicorn)
   end
 end
 
-# set default directory for multiproces metrics gathering
-ENV['prometheus_multiproc_dir'] ||= 'tmp/prometheus_multiproc_dir'
-
 require ::File.expand_path('../config/environment',  __FILE__)
 
 map ENV['RAILS_RELATIVE_URL_ROOT'] || "/" do

config/boot.rb

@@ -5,6 +5,9 @@ ENV['BUNDLE_GEMFILE'] ||= File.expand_path('../../Gemfile', __FILE__)
 
 require 'bundler/setup' if File.exist?(ENV['BUNDLE_GEMFILE'])
 
+# set default directory for multiproces metrics gathering
+ENV['prometheus_multiproc_dir'] ||= 'tmp/prometheus_multiproc_dir'
+
 # Default Bootsnap configuration from https://github.com/Shopify/bootsnap#usage
 require 'bootsnap'
 Bootsnap.setup(