Add Pi signage Phase 1 player artifacts

Squash merge Sprint 14 Pi signage player artifacts.

apps/fc-signage-pi-player/scripts/flowercore-signage-prelaunch.sh

@@ -0,0 +1,20 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+mkdir -p /var/log/fc-signage-player
+
+for f in /etc/flowercore/signage-node.json /etc/fc-signage-player/client.p12 /etc/fc-signage-player/client.p12.pass; do
+  if [[ ! -r "$f" ]]; then
+    echo "[$(date -Is)] prelaunch: missing or unreadable $f" >&2
+    exit 1
+  fi
+done
+
+if openssl pkcs12 -in /etc/fc-signage-player/client.p12 -passin file:/etc/fc-signage-player/client.p12.pass -nokeys -clcerts 2>/dev/null \
+   | openssl x509 -checkend $((7*24*3600)) -noout; then
+  :
+else
+  echo "[$(date -Is)] prelaunch: client cert expires within 7 days" >&2
+fi
+
+echo "[$(date -Is)] prelaunch: ok" | tee -a /var/log/fc-signage-player/prelaunch.log