Allow installing Python packages system-wide in Docker again

Dockerfile

@@ -64,6 +64,7 @@ RUN set -e; \
              ${ALEKSIS_static__root} \
              ${ALEKSIS_media__root} \
              ${ALEKSIS_backup__location}; \
+    dpkg-divert --rename --add /usr/lib/$(py3versions -d)/EXTERNALLY-MANAGED; \
     eatmydata pip install AlekSIS-Core\[$EXTRAS\]$APP_VERSION
 
 # Define entrypoint, volumes and uWSGI running on port 8000