✅(e2e) test the pdf export of the impress app

Add a test to check the pdf export of the
impress app.
It intercept the download of the PDF and
read its content.
We can assert that the template is correctly
rendered, and that the pad text is present as
well.

Makefile

@@ -203,9 +203,10 @@ dbshell: ## connect to database shell
 	docker compose exec app-dev python manage.py dbshell
 .PHONY: dbshell
 
+resetdb: FLUSH_ARGS ?=
 resetdb: ## flush database and create a superuser "admin"
 	@echo "$(BOLD)Flush database$(RESET)"
-	@$(MANAGE) flush
+	@$(MANAGE) flush $(FLUSH_ARGS)
 	@${MAKE} superuser
 .PHONY: resetdb