🗃️(backend) export to docx

We can now export our document to a docx file.
This is done by converting the html to a docx
file using the pypandoc and pandoc library.
We added the "format" param to the
generate-document endpoint, "format" accept
"pdf" or "docx" as value.

.github/workflows/impress.yml

@@ -198,7 +198,7 @@ jobs:
       - name: Install gettext (required to compile messages)
         run: |
           sudo apt-get update
-          sudo apt-get install -y gettext
+          sudo apt-get install -y gettext pandoc
 
       - name: Generate a MO file from strings extracted from the project
         run: python manage.py compilemessages