Automate population of parts in `_make_pdf.qmd`

Right now we have to manually add/update list elements in [this list](https://github.com/Openscapes/series/blob/89d25511eac78f8dd679b051b7cb32ea91bc0305/_make_pdf.qmd?plain=1#L62) to include a doc in the pdf. We should be able to automate this by reading the `_quarto.yml`.