added gotify alerts on image updates

podman/files/check_image_updates.service.jinja

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+[Unit]
+Description=Check for image updates on configured podman containers
+
+[Service]
+Type=oneshot
+User={{ pillar.podman.user }}
+ExecStart={{ salt['user.info'](pillar.podman.user).home }}/bin/check_image_updates.sh
+
+[Install]
+WantedBy=default.target

podman/files/check_image_updates.sh.jinja

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+#!/usr/bin/env bash
+
+URL="{{ pillar['podman']['gotify']['url'] }}"
+TOKEN="{{ pillar['podman']['gotify']['token'] }}"
+TITLE="Updates on $HOSTNAME"
+PRIORITY="{{ pillar['podman']['gotify']['priority'] }}"
+
+{% raw -%}
+function check_update(){
+    IFS=',' read -r -a container_info <<< "$(podman container inspect $1 --format '{{ .Name }},{{ .ImageName }},{{ .Image }}')"
+
+    podman pull "${container_info[1]}"
+    if [[ "$(podman image inspect "${container_info[1]}" --format "{{.Id}}")" != "${container_info[2]}" ]];then
+        containers[${#containers[@]}]="${container_info[0]}"
+    fi
+}
+
+
+IFS=$'\n'
+for line in $(podman container ls -q); do
+    check_update "$line"
+done
+if [[ "${#containers[@]}" == "0" ]]; then
+    exit
+fi
+
+MESSAGE=$(cat << EOM
+Following ${#containers[@]} container(s) has updates:
+${containers[*]}
+EOM
+)
+
+curl "$URL/message?token=$TOKEN" -F "title=$TITLE" -F "priority=$PRIORITY" -F "message=$MESSAGE"
+echo " "
+{% endraw -%}

podman/files/check_image_updates.timer.jinja

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+[Unit]
+Description=Restic backup timer
+
+[Timer]
+OnCalendar=Sun, 12:00
+Unit=check_image_updates.service
+
+[Install]
+WantedBy=timers.target