Arxiv submission may need \pdfoutput=1 in the preamble

Hello, as I reported in https://github.com/rstudio/rmarkdown/issues/2315, Arxiv sometimes fails to recognize a submitted document as a PDFLaTeX, consequently not showing the material in the final output; for example this happens if no images are linked in the .tex file.
To force recognition by the arxiv system one has to add \pdfoutput=1 in the first 5 lines of the .tex file preamble (see https://arxiv.org/help/submit_tex).

The rticles::arxiv_article() template does not provide such option.

I suggest either adding \pdfoutput=1 at the beginning of the template or, if you think there could be reasons to use such options, conditioning the option to a flag in the YAML.

I can take care of it once agreed on the implementation.

Start by locating the rticles::arxiv_article() template and reviewing the linked arXiv submission guidance. Decide whether the generated preamble should always include \pdfoutput=1 or expose it through YAML, then verify that the resulting .tex file places the setting within its first five lines.