tools: Add script to update `stable` tag on Dockerhub

diff --git a/tools/promote-stable.sh b/tools/promote-stable.sh
new file mode 100644
index 00000000..f3efddd6
--- /dev/null
+++ b/tools/promote-stable.sh
@@ -0,0 +1,46 @@
+#!/bin/bash
+# DOCKER_USERNAME=<your-username> DOCKER_PASSWORD=<your-password> source ./tools/promote-stable.sh
+
+IMAGE_NAME="elementsproject/lightningd"
+MINIMUM_DAYS_BEFORE_STABLE=15
+
+if [ -z "$DOCKER_USERNAME" ] || [ -z "$DOCKER_PASSWORD" ]; then
+  echo "❌ Oops! Looks like someone forgot their Docker Hub credentials at home!"
+  echo "🔑 Please set DOCKER_USERNAME and DOCKER_PASSWORD as environment variables."
+  echo "💡 Hint: We can't log in with 'your-username' and 'your-password' (nice try though!)"
+  return 1 2>/dev/null || exit 1
+fi
+
+# Get Docker image information
+DOCKER_TOKEN=$(curl -s -H "Content-Type: application/json" -X POST -d "{\"username\": \"$DOCKER_USERNAME\", \"password\": \"$DOCKER_PASSWORD\"}" \
+  https://hub.docker.com/v2/users/login/ | jq -r .token)
+LATEST_INFO=$(curl -s -H "Authorization: JWT $DOCKER_TOKEN" https://hub.docker.com/v2/repositories/${IMAGE_NAME}/tags/latest/)
+LAST_UPDATED=$(echo "$LATEST_INFO" | jq -r .last_updated) || 0
+DAYS_OLD=$(( ($(date +%s) - $(date -d "$LAST_UPDATED" +%s)) / 86400 ))
+
+if [ $DAYS_OLD -ge $MINIMUM_DAYS_BEFORE_STABLE ]; then
+  echo "🎂 Ah, the latest tag has aged beautifully for $DAYS_OLD days, like a perfectly fermented sourdough!"
+  echo "📦 Time for its grand debut as 'stable'..."
+  echo ""
+  docker buildx imagetools create --tag $IMAGE_NAME:stable $IMAGE_NAME:latest
+  echo ""
+  echo "✅ 🎉 Congratulations! Your image has officially graduated to stable status!"
+else
+  DAYS_REMAINING=$((MINIMUM_DAYS_BEFORE_STABLE - DAYS_OLD))
+  echo "⏰ Whoa there! This latest tag is only $DAYS_OLD days old."
+  echo "🧀 It's like cheese - it needs time to mature! Wait for $DAYS_REMAINING more day(s)..."
+  read -p "❓ But hey, it's your rodeo. Still want to promote it to stable? (y/n): " -n 1 -r
+  echo ""
+  
+  if [[ $REPLY =~ ^[Yy]$ ]]; then
+    echo "🤠 Living dangerously, I see! Alright, throwing caution to the wind..."
+    echo "🚀 Strapping rockets to this latest image and sending it to stable anyway!"
+    echo ""
+    docker buildx imagetools create --tag $IMAGE_NAME:stable $IMAGE_NAME:latest
+    echo ""
+    echo "✅ 💥 Done! Let's hope this doesn't come back to haunt us..."
+  else
+    echo "🎯 Smart move! Your reputation as the cautious one remains intact."
+    echo "☕ Grab a coffee, touch some grass, and revisit this in $DAYS_REMAINING day(s)."
+  fi
+fi