Remove metrics group in Gemfile

Move the metrics gems out of the group since these are installed all the
time anyway.

Prometheus client in particular is required to boot the application.

Gemfile

@@ -335,13 +335,9 @@ gem 'peek', '~> 1.1'
 gem 'snowplow-tracker', '~> 0.6.1'
 
 # Metrics
-group :metrics do
-  gem 'method_source', '~> 1.0', require: false
-  gem 'webrick', '~> 1.6.1', require: false
-
-  # Prometheus
-  gem 'prometheus-client-mmap', '~> 0.12.0'
-end
+gem 'method_source', '~> 1.0', require: false
+gem 'webrick', '~> 1.6.1', require: false
+gem 'prometheus-client-mmap', '~> 0.12.0', require: 'prometheus/client'
 
 group :development do
   gem 'lefthook', '~> 0.7.0', require: false

config/initializers/7_prometheus_metrics.rb

 # frozen_string_literal: true
 
-require 'prometheus/client'
-
 # Keep separate directories for separate processes
 def prometheus_default_multiproc_dir
   return unless Rails.env.development? || Rails.env.test?

lib/gitlab/metrics/exporter/base_exporter.rb

 # frozen_string_literal: true
 
+require 'webrick'
+require 'prometheus/client/rack/exporter'
+
 module Gitlab
   module Metrics
     module Exporter

lib/gitlab/metrics/exporter/sidekiq_exporter.rb

 # frozen_string_literal: true
 
-require 'webrick'
-require 'prometheus/client/rack/exporter'
-
 module Gitlab
   module Metrics
     module Exporter

lib/gitlab/metrics/exporter/web_exporter.rb

 # frozen_string_literal: true
 
-require 'webrick'
-require 'prometheus/client/rack/exporter'
-
 module Gitlab
   module Metrics
     module Exporter

lib/gitlab/metrics/prometheus.rb

 # frozen_string_literal: true
 
-require 'prometheus/client'
-
 module Gitlab
   module Metrics
     module Prometheus