Add tsdb startup duration metric (#7737)
Add tsdb startup duration metric (#7737)

* Add tsdb wal replay duration metric

Signed-off-by: Max Neverov <2e3e0b537870d2db9db00b2a24b33f2548fcb778@gmail.com>
prometheus/prometheus,prometheus/prometheus,keegancsmith/prometheus,alileza/prometheus,GoogleCloudPlatform/prometheus,alileza/prometheus,GoogleCloudPlatform/prometheus,alileza/prometheus,alileza/prometheus,keegancsmith/prometheus,alileza/prometheus,GoogleCloudPlatform/prometheus,keegancsmith/prometheus,keegancsmith/prometheus,prometheus/prometheus,prometheus/prometheus,GoogleCloudPlatform/prometheus,keegancsmith/prometheus,prometheus/prometheus,GoogleCloudPlatform/prometheus