Permit Symbol being serialized

Rails decided to deem Symbol safe so we can too.

April reported not being able to update CMS pages.  I was able to reproduce in development environment.

```
Completed 500 Internal Server Error in 235ms (ActiveRecord: 46.5ms | Allocations: 89677)

Psych::DisallowedClass (Tried to load unspecified class: Symbol):

comfortable-mexican-sofa (456fb8507e96) app/controllers/comfy/admin/cms/pages_controller.rb:49:in `update'
```

Left breadcrumbs so that we can clean this up with patched version of Rails

Gemfile

@@ -1,6 +1,7 @@
 source 'https://rubygems.org'
 
 # Bundle edge Rails instead: gem 'rails', github: 'rails/rails'
+# TODO: revisit config.active_record.yaml_column_permitted_classes when this gets bumped
 gem 'rails', '~> 7.0.3'
 # Use sqlite3 as the database for Active Record
 gem 'sqlite3'

config/application.rb

@@ -22,5 +22,9 @@ class Application < Rails::Application
     #
     # config.time_zone = "Central Time (US & Canada)"
     # config.eager_load_paths << Rails.root.join("extras")
+
+    # Rails decided to deem Symbol safe
+    # https://github.com/rails/rails/pull/45584
+    config.active_record.yaml_column_permitted_classes = [Symbol]
   end
 end