Runtime SSL certificate hot reload without restart

Feature Request

Currently, SSLApp only accepts key_file_name and cert_file_name during initialization. Once the certificate expires (e.g., Let's Encrypt 90-day certs), the entire Node.js process must be restarted to load the new certificate.

Use Case

• Using Let's Encrypt with automatic renewal
• Running WebSocket servers with long-lived connections
• Need zero-downtime certificate rotation
• Production environments where process restart is costly

Proposed API

const app = uWS.SSLApp({
  key_file_name: '/path/to/key.pem',
  cert_file_name: '/path/to/cert.pem'
});

// After certbot renews the certificate:
app.updateSSL({
  key_file_name: '/path/to/key.pem',
  cert_file_name: '/path/to/cert.pem'
});

Start by tracing how SSLApp consumes key_file_name and cert_file_name during initialization, then identify the runtime SSL state that would need to change. Define and validate the proposed updateSSL API, including certificate rotation for long-lived WebSocket servers, and verify that renewed certificates load without restarting the Node.js process.