Python Script to Monitor Website Uptime and Send Alerts

Write a Python script that monitors website uptime and sends alerts when a site goes down. Features: (1) **Config file (YAML)**: Define multiple websites to monitor, each with: URL, expected status code, check interval (seconds), timeout, and alert contacts. (2) **Health checks**: HTTP GET with configurable timeout, verify SSL certificates, check response time against a threshold (e.g., alert if >3 seconds). (3) **State tracking**: Keep track of consecutive failures — only alert after 3 consecutive failures to avoid false positives. Track uptime percentage over rolling 24 hours. (4) **Alerts**: Send notifications via email (SMTP) and optional Slack webhook. Include: which site is down, since when, last successful check, and error details. (5) **Recovery notification**: Alert when a site comes back up with downtime duration. (6) **Logging**: Structured JSON logs with rotation. (7) **Dashboard output**: Generate a simple HTML status page showing all monitored sites with uptime percentages. (8) Use asyncio for concurrent checks. Include requirements.txt and a sample config.yaml.