Channel supervisor for reckon-gater PubSub API SET

Supervises all 10 channel implementations: - esdb_channel_events (high priority) - esdb_channel_health (high priority) - esdb_channel_alerts (critical, HMAC required) - esdb_channel_security (critical, HMAC required) - esdb_channel_system (normal priority) - esdb_channel_metrics (normal priority) - esdb_channel_audit (normal priority) - esdb_channel_lifecycle (normal priority) - esdb_channel_logging (low priority) - esdb_channel_diagnostics (low priority)