ClickHouse: enable built-in Prometheus exporter at :9363/metrics via
config.d/prometheus.xml with metrics, events, and async_metrics.
Docker labels added for docker_sd_configs auto-discovery.
Tenant servers: add prometheus.scrape/path/port labels to provisioned
server containers pointing to /api/v1/prometheus:8081.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>