Improve PDF export method

[johnmeshulam]

Currently, not only is there a memory leak (#728 ), the process is also extremely slow.

Ideas for tasks

• Make puppeteer use non root user and remove --no-sandbox argument
• We wait for the PDF download then send a file response. Is it possible to make this process faster and change the way we export the PDFs?

[johnmeshulam]

Closing this since the latest PR fixed the memory leak and also improved performance