Integrate rack-mini-profiler.

app/Gemfile

@@ -26,6 +26,7 @@ group :development, :test do
   gem 'factory_bot_rails'
   gem 'faker'
   gem 'haml_lint', require: false
+  gem 'rack-mini-profiler', require: false
   gem 'rspec-rails', require: false
   gem 'rubocop', require: false
   gem 'rubocop-factory_bot', require: false

app/Gemfile.lock

@@ -234,6 +234,8 @@ GEM
       nio4r (~> 2.0)
     racc (1.8.1)
     rack (3.1.7)
+    rack-mini-profiler (3.3.1)
+      rack (>= 1.2.0)
     rack-protection (4.0.0)
       base64 (>= 0.1.0)
       rack (>= 3.0.0, < 4)
@@ -381,6 +383,7 @@ DEPENDENCIES
   pg
   propshaft
   puma
+  rack-mini-profiler
   rails
   rails_autolink
   rspec-rails

app/config/initializers/rack_mini_profiler.rb

@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+if Rails.env.development?
+  require 'rack-mini-profiler'
+
+  # The initializer was required late, so initialize it manually.
+  Rack::MiniProfilerRails.initialize!(Rails.application)
+end