Enhancement: include current filename placeholder in workflows (#8319)

Co-authored-by: Trenton H <797416+stumpylog@users.noreply.github.com>
Co-authored-by: shamoon <4887959+shamoon@users.noreply.github.com>

src/documents/serialisers.py

@@ -1917,6 +1917,7 @@ class WorkflowActionSerializer(serializers.ModelSerializer):
                         added_time="",
                         owner_username="",
                         original_filename="",
+                        filename="",
                         created="",
                         created_year="",
                         created_year_short="",