[DBBackup] Switch to Debian sid image for Mongo client

pica-db-backup/CHANGELOG.md

 ## Version 1.3
 
-* Switch from Python image to Bullseye image
+* Switch from Python image to Sid image (because Mongo does not exists in Bullseye and PG12 only in Bullseye and Sid...)
 * Update for PG12+
 * Default cron hour at 03:00AM

pica-db-backup/Dockerfile

-FROM debian:bullseye-slim
+FROM debian:sid-slim
 
 RUN apt-get update && \
     apt-get install -y --no-install-recommends \