Add client-side experiment for NPD Health Monitoring config (google#525)

* add experiment flag for health monitoring

* fix log comment

Author: jessieqliu

launcher/container_runner.go

@@ -129,8 +129,15 @@ func NewRunner(ctx context.Context, cdClient *containerd.Client, token oauth2.To
 		return nil, err
 	}
 
-	if err := enableMonitoring(launchSpec.MonitoringEnabled, logger); err != nil {
-		return nil, err
+	if launchSpec.MonitoringEnabled == spec.All && !launchSpec.Experiments.EnableHealthMonitoring {
+		logger.Info("Health Monitoring experiment is not enabled - falling back to memory-only.")
+		if err := enableMonitoring(spec.MemoryOnly, logger); err != nil {
+			return nil, err
+		}
+	} else {
+		if err := enableMonitoring(launchSpec.MonitoringEnabled, logger); err != nil {
+			return nil, err
+		}
 	}
 
 	logger.Info(fmt.Sprintf("Launch Policy              : %+v\n", launchPolicy))

launcher/internal/experiments/experiments.go

@@ -13,6 +13,7 @@ import (
 type Experiments struct {
 	EnableTestFeatureForImage bool
 	EnableTempFSMount         bool
+	EnableHealthMonitoring    bool
 }
 
 // New takes a filepath, opens the file, and calls ReadJsonInput with the contents