WIP: windmill derived image builds successfully, adding rootless + read-only

Agent-Logs-Url: https://github.com/nextcloud/all-in-one/sessions/6f198732-63c3-41b7-8b2e-1b5fa565ee21

Co-authored-by: szaimen <42591237+szaimen@users.noreply.github.com>

Containers/windmill/windmill-start.sh

@@ -0,0 +1,10 @@
+#!/bin/bash
+
+# Wait for PostgreSQL to accept connections
+until pg_isready -h localhost -q 2>/dev/null; do
+    echo "Waiting for PostgreSQL to be ready..."
+    sleep 2
+done
+
+# Start Windmill
+exec windmill