Use supervisord to supervise Postgres and Caddy in the Complement image. (#12480)

changelog.d/12480.misc

docker/Dockerfile-workers

docker/complement/SynapseWorkers.Dockerfile

docker/complement/conf-workers/caddy.supervisord.conf

docker/complement/conf-workers/postgres.supervisord.conf

...mplement/conf-workers/start-complement-synapse-workers.sh

docker/conf/log.config

docker/configure_workers_and_start.py

docker/prefix-log