Permit applications to hack in custom DB config for ActionText::RichText until AT has first-class multi-DB support:
ActiveSupport.on_load(:action_text_record) do
connects_to reading: :action_text_replica, writing: :action_text_primary
end
Failing test before the ActionText::RichText change:
```
Error:
ActionText::ModelTest#test_embed_extraction_only_extracts_file_attachments:
ArgumentError: Could not find or build blob: expected attachable, got #<ActionText::Attachables::RemoteImage:0x00007fb0259fef70 @url="http://example.com/cat.jpg", @content_type="image", @width=nil, @height=nil>
```
