Support alternatives to short-title #12
Description
Unlike MyST, Quarto does not have a short_title field. They do however have8 a few different alternative titles](https://quarto.org/docs/authoring/title-blocks.html#metadata-labels). It would be great to support one of these being read as the short-title field, so it can be rendered with pubmatter.show-page-header(fm). Otherwise, as far as I can tell, Quarto users are currently stuck with the full title in the header.