Migrate Markdown PDF, MD, TXT Export functionality to the Frontend

[devleejb]

What would you like to be added:
Currently, the Markdown PDF, MD, and TXT Export functionalities are implemented on the backend side. However, as we are migrating to Go for the backend, implementing these features on the Go side is becoming challenging. Given that there are many open-source tools available in the TypeScript environment, I propose moving the implementation of these export functionalities to the frontend.

Why is this needed:
This migration will allow for more flexibility and accessibility in utilizing TypeScript-based libraries for document export functionality, ensuring that we can continue to provide these features efficiently without the complications arising from the Go migration.