[Etherpad] Add nano to final image to easy testing

pica-etherpad/Dockerfile

@@ -60,7 +60,7 @@ RUN useradd --uid ${UID} --create-home etherpad
 COPY --from=downloader --chown=etherpad /opt/etherpad-lite /opt/etherpad-lite/
 
 RUN apt-get update && \
-    apt-get install -y curl default-mysql-client postgresql-client && \
+    apt-get install -y curl nano default-mysql-client postgresql-client && \
     chmod +x /opt/etherpad-lite/entrypoint.sh && \
     usermod -d /opt/etherpad-lite etherpad && \
     chown -R etherpad /opt/etherpad-lite && \