Transitions the Docker image to use s6 and s6-overlay for process supervision instead of supervisord (#8886)

docker/rootfs/etc/s6-overlay/s6-rc.d/svc-flower/run

@@ -0,0 +1,24 @@
+#!/command/with-contenv /usr/bin/bash
+# shellcheck shell=bash
+
+declare -r log_prefix="[svc-flower]"
+
+echo "${log_prefix} Checking if we should start flower..."
+
+if [[ -n "${PAPERLESS_ENABLE_FLOWER}" ]]; then
+	# Small delay to allow celery to be up first
+	echo "${log_prefix} Starting flower in 5s"
+	sleep 5
+	cd ${PAPERLESS_SRC_DIR}
+
+	if [[ -n "${USER_IS_NON_ROOT}" ]]; then
+		exec /usr/local/bin/celery --app paperless flower --conf=${PAPERLESS_SRC_DIR}/paperless/flowerconfig.py
+	else
+		exec s6-setuidgid paperless /usr/local/bin/celery --app paperless flower --conf=${PAPERLESS_SRC_DIR}/paperless/flowerconfig.py
+	fi
+
+else
+	echo "${log_prefix} Not starting flower"
+	# https://skarnet.org/software/s6/s6-svc.html
+	s6-svc -Od .
+fi

docker/rootfs/etc/s6-overlay/s6-rc.d/svc-flower/type

@@ -0,0 +1 @@
+longrun