Add basic metrics (#2792)

* fix some log output

* add from_unixtime and unix_timestamp

* add metrics package

* metric option from env

* do not expose prom at top layer

* add some system vars

* move reserved labels to MetricFamily

* add more test

* adjust unixEpoch

* remove SV bool check

* add collectorToProm interface

* use rateCounter for now

* add grafana dashboard json

* fix merge conflict

* add a temp config to force drop-and-init

* fix time test

* fix ut error

* fix unixtimestamp test

* make static check happier

* larger collector buf