func EnableHandlingTimeHistogram(opts ...HistogramOption) {
	DefaultServerMetrics.EnableHandlingTimeHistogram(opts...)
	prom.Register(DefaultServerMetrics.serverHandledHistogram)
}
EnableHandlingTimeHistogram turns on recording of handling time
of RPCs. Histogram metrics can be very expensive for Prometheus
to retain and query. This function acts on the DefaultServerMetrics
variable and the default Prometheus metrics registry.
package grpc_prometheus
import (
	prom "github.com/prometheus/client_golang/prometheus"
	"google.golang.org/grpc"
)
var (
	DefaultServerMetrics = NewServerMetrics()
	UnaryServerInterceptor = DefaultServerMetrics.UnaryServerInterceptor()
	StreamServerInterceptor = DefaultServerMetrics.StreamServerInterceptor()
)
func init() {
	prom.MustRegister(DefaultServerMetrics.serverStartedCounter)
	prom.MustRegister(DefaultServerMetrics.serverHandledCounter)
	prom.MustRegister(DefaultServerMetrics.serverStreamMsgReceived)
	prom.MustRegister(DefaultServerMetrics.serverStreamMsgSent)
}
func Register(server *grpc.Server) {
	DefaultServerMetrics.InitializeMetrics(server)
}