* initial commit for prometheus and sys/metrics support
* Throw an error if prometheusRetentionTime is 0,add prometheus in devmode
* return when format=prometheus is used and prom is disable
* parse prometheus_retention_time from string instead of int
* Initialize config.Telemetry if nil
* address PR issues
* add sys/metrics framework.Path in a factory
* Apply requiredMountTable entries's MountConfig to existing core table
* address pr comments
* enable prometheus sink by default
* Move Metric-related code in a separate metricsutil helper
