addItem appends or inserts any supported Forms item.
Example
Inputs
form and item are required. position is a one-based insertion position;
omit it to append. requiredRevisionId enables optimistic concurrency.
Item types
question:title, optionaldescription/grading, and a typedquestionfrom Add question.grid:columns,gridType: "multipleChoice" | "checkbox", and rows withtitle, optionalrequiredandquestionId;shuffleRowsis optional.pageBreakortext: optionaltitleanddescription.image: publicsourceUrl, optionalaltText,alignment,width1–740, title, and description.video: YouTubeyoutubeUrl, optionalcaption,alignment,width1–740, title, and description.
account optionally selects the Google account binding.
Output
Returns the complete updatedForm, including provider-generated IDs. Images
must be reachable by Google and videos must use a YouTube watch or share URL.