onFormChanged watches schema-level changes and emits the current complete form
along with the provider notification metadata.
Example
Options
form: string is required and accepts a static ID or standard Forms URL.
account is an optional static Google account binding.
Trigger data
form. This trigger subscribes to SCHEMA notifications, so its eventType is
normally "SCHEMA". Notifications signal that something changed; compare the
current form or its revisionId with stored state when you need a field-level
diff.