chore: include $CIRCLE_BUILD_URL in the slack message

this will help us easily reach the failed CircleCI job from Slack

Author: Shesekino

scripts/slack-notify-failure.sh

@@ -3,4 +3,4 @@
 BRANCH_NAME="$1"
 NOTIFICATION_COLOR=${2:-#EE0000}
 
-curl -X POST -H 'Content-Type:application/json' -d '{"attachments": [{"color": "'$NOTIFICATION_COLOR'", "fallback": "Build Notification: '$CIRCLE_BUILD_URL'", "title": ":warning: Kubernetes-Monitor Merge Failure :warning:", "text": ":egg_broken_1: Kubernetes-Monitor broken branch: `'$BRANCH_NAME'` :egg_broken_1:"}]}' $SLACK_WEBHOOK
+curl -X POST -H 'Content-Type:application/json' -d '{"attachments": [{"color": "'$NOTIFICATION_COLOR'", "fallback": "Build Notification: '$CIRCLE_BUILD_URL'", "title": ":warning: Kubernetes-Monitor Merge Failure :warning:", "text": ":egg_broken_1: Kubernetes-Monitor broken branch: `'$BRANCH_NAME'` :egg_broken_1:\n'$CIRCLE_BUILD_URL'"}]}' $SLACK_WEBHOOK