Highlight risk of fields displaying in SiteTree due to scaffolding

[GuySartorelli]

There is a fairly sizable risk that people have sensitive form fields in their pages that should only be shown if some condition is true, e.g. a permission check.

Right now, if the condition is false it's a no-op and the field won't be displayed.
For CMS 6 a no-op results in the form being scaffolded. Devs will need to either:

1. flip the condition, so if it's true there's a no-op (or they update the field) and if it's false they explicitly remove the field, or
2. use the scaffold_cms_fields_settings config to tell framework to explicitly not scaffold the form (and leave the condition as it is)

Acceptance Criteria

• A new > [!WARNING] block is added to the "SiteTree uses form field scaffolding" section of the 6.0.0 changelog calling out the risk, and giving some advice about how to resolve it.