[Fix rubocop#796] Add several directories to Exclude

Fixes rubocop#796.

This PR adds several directories to `Exclude` to prevent slow investigation.
These directories (`log`, `public`, and `storage`) provided by `bin/rails`
are expected not to contain Ruby code. And `tmp` and `vendor` directories
have already been excluded in the RuboCop core.
https://github.com/rubocop/rubocop/blob/v1.36.0/config/default.yml#L65-L66

Author: koic

changelog/change_add_several_dir_to_exclude_to_prevent_slow_investigation.md

@@ -0,0 +1 @@
+* [#796](https://github.com/rubocop/rubocop-rails/issues/796): Add several directories to `Exclude` to prevent slow investigation. ([@koic][])

config/default.yml

@@ -10,6 +10,9 @@ AllCops:
     # Exclude db/schema.rb and db/[CONFIGURATION_NAMESPACE]_schema.rb by default.
     # See: https://guides.rubyonrails.org/active_record_multiple_databases.html#setting-up-your-application
     - db/*schema.rb
+    - log/**/*
+    - public/**/*
+    - storage/**/*
   # Enable checking Active Support extensions.
   # See: https://docs.rubocop.org/rubocop/configuration.html#enable-checking-active-support-extensions
   ActiveSupportExtensionsEnabled: true