Allow has_and_belongs_to_many to reduce code

The Rails/HasAndBelongsToMany rule wants model classes for all
many-to-many relationship tables in the database. But our team thinks
that it's useful to declare has_and_belongs_to_many relationships which
don't require an additional model.

.rubocop_styleguide.yml

@@ -53,6 +53,13 @@ Rails/ApplicationRecord:
     # Migrations should not contain application code:
     - "db/migrate/*.rb"
 
+# Allow many-to-many associations without explicit model.
+# - It avoids the additional code of a model class.
+# - It simplifies the declaration of the association.
+# - Rails may know that there are no callbacks associated.
+Rails/HasAndBelongsToMany:
+  Enabled: false
+
 Rails/SkipsModelValidations:
   AllowedMethods:
     - "touch"

.rubocop_todo.yml

@@ -419,19 +419,6 @@ Rails/ActiveRecordOverride:
   Exclude:
     - 'app/models/spree/product.rb'
 
-# Offense count: 8
-# Configuration parameters: Include.
-# Include: app/models/**/*.rb
-Rails/HasAndBelongsToMany:
-  Exclude:
-    - 'app/models/enterprise.rb'
-    - 'app/models/enterprise_group.rb'
-    - 'app/models/order_cycle.rb'
-    - 'app/models/spree/role.rb'
-    - 'app/models/spree/shipping_method.rb'
-    - 'app/models/spree/user.rb'
-    - 'app/models/spree/zone.rb'
-
 # Offense count: 47
 # Configuration parameters: Include.
 # Include: app/models/**/*.rb