[WIP] Fix comments export in .odt, .PDF, and markdown files

[Copilot]

Thanks for asking me to work on this. I will get started on it and keep this PR's description up to date as I form a plan and make progress.

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This section details on the original issue you should resolve

<issue_title>Comments are not exported when exporting to .odt, .PDF or markdown files</issue_title>
<issue_description>I suppose figuring out a way to represent comments in markdown could be tricky, but leaving them out when exporting to rich formats like OpenDocument (ODT) and PDF is some pretty serious data loss that can undermine users' trust in the system; they may not notice until it is too late when they reopen the exported document after the etherpad instance is gone/expired...</issue_description>

Comments on the Issue (you are @copilot in this section)

@JohnMcLear I agree re odt, we love our libre office brothers and sisters. But pdf.... Do Adobe even have an open spec for this?!

Does soffice.bin have support for comments in html to odt? If so, point me at the docs and I will make sure the html we pass to soffice is compliant.

Fwiw we pass html from etherpad to soffice which is a libre office tool for converting files :)</comment_new>