changes blob json for all ActiveStorage attachments

[jonknapp]

Not sure if this fits as a bug or an unexpected side-effect, but I use blob.as_json(only: allowed_fields) as part of an API. After we added lexxy, we found that it started injecting additional fields (url and previewable) for any active storage attachments. I'd assume the code at

lexxy/lib/active_storage/blob_with_preview_url.rb

Line 11 in ad2c9eb

preview(resize_to_limit: PREVIEW_SIZE), ActiveStorage::Current.url_options.merge(only_path: true)

is helpful for use of attachments within lexxy, but it was a surprise to see this effect code outside of a rich text field and it's attachments.