feat: add support to export to PDF

[mhadaily]

Description

Well, it's nice to have a PDF version of the slides both as backup and also printable if needed.

Requirements

• [ ] Checklist of requirements to be fulfilled

Additional Context

It's quite common to receive a PDF of slides from another system to to catch up, it's nice to have this feature.

[mkobuolys]

I discussed this and I am still trying to grasp the real issue there. Having the current environment in mind, when is the printable version of slides actually needed?

[mhadaily]

I know speakers like to take notes on paper while presenting. Printable necessarily has little demand, though PDF could be a good option for offline and backup plans. However, if you can provide a print button on each slide for speakers only to print their HTML page, that would suffice, or one button for speakers so that they can download all slides into one PDF.