New `set_item_description_content` mutation

You can now use the set_item_description_content mutation to update an item’s description via the API. The description is provided as Markdown, which is then converted into document blocks that replace the item’s existing content.

mutation {
  set_item_description_content(
    item_id: 1234567890
    markdown: "**The updated description!**"
  ) {
    success
    error
    block_ids
  }
}