Add AuthenticationGenerator for users factory creation

This change addresses an issue where running the `factory_bot` generator could result in a `factory_bot [not found]` error.
The problem occurred due to missing generator definitions and template files.

With this update, the authentication generator is properly defined and includes the necessary templates, ensuring that the `users.rb` factory file is generated regardless of whether the project is using RSpec (`spec/factories`) or Minitest (`test/factories`).
This guarantees consistent behavior and avoids generator errors in environments without a `spec` directory.

Previously, projects without a `spec` directory or with incomplete generator/template setup would fail when invoking `factory_bot` generators, making it impossible to scaffold the necessary factory files automatically.

- Added the missing `factory_bot:authentication` generator definition.
- Included `users.rb` template under `templates` directory.
- Implemented logic to detect the test framework and place the generated factory file in the correct directory (`spec/factories` or `test/factories`).
- Ensured generator runs successfully regardless of the presence of a `spec` directory.

Author: rodrigotoledo

lib/generators/factory_bot/authentication/authentication_generator.rb

@@ -0,0 +1,34 @@
+# frozen_string_literal: true
+
+require "generators/factory_bot"
+require "factory_bot_rails"
+require "fileutils"
+
+module FactoryBot
+  module Generators
+    class AuthenticationGenerator < Base
+      def create_users_factory
+        dir = factories_dir
+        FileUtils.mkdir_p(dir)
+
+        target = File.join(dir, "users.rb")
+        if File.exist?(target)
+          say_status :skip, "users.rb already exists at #{target}", :yellow
+        else
+          template "users.rb", target
+          say_status :create, target, :green
+        end
+      end
+
+      private
+
+      def factories_dir
+        if Dir.exist?(Rails.root.join("spec"))
+          Rails.root.join("spec", "factories").to_s
+        else
+          Rails.root.join("test", "factories").to_s
+        end
+      end
+    end
+  end
+end

lib/generators/factory_bot/authentication/templates/users.rb

@@ -0,0 +1,9 @@
+# frozen_string_literal: true
+
+FactoryBot.define do
+  factory :user do
+    password { "password123" }
+    password_confirmation { "password123" }
+    email_address { "user#{SecureRandom.hex(3)}@example.com" }
+  end
+end