* add configuration options to enable the NATS server HTTP monitoring
endpoint:
- NATS_MONITORING_ENABLED (defaults to false)
- NATS_MONITORING_HTTP_HOST (defaults to 127.0.0.1)
- NATS_MONITORING_HTTP_PORT (defaults to 8222)
- NATS_MONITORING_ENABLE_TLS (defaults to false)
Fixes#3294