More structured logging for Task object

also downgrade log message 'Adding a state change event to send' to
DEBUG from INFO, since this log message is redundantly logged twice
whenever there is a state change, since we also log the state change
when we send it to ECS, like this:

```
level=info time=2023-05-05T22:17:23Z msg="TaskHandler: Adding a state change event to send batched container/managed agent events: arn:aws:ecs:us-west-2:039193556298:task/usw2/0b670ab4398f4f138e1bad9293f563a0 -> RUNNING, Known Sent: RUNNING, PullStartedAt: 2023-05-05 22:16:44.14108352 +0000 UTC m=+435.253624196, PullStoppedAt: 2023-05-05 22:16:44.3532973 +0000 UTC m=+435.465837967, ExecutionStoppedAt: 0001-01-01 00:00:00 +0000 UTC" module=task_handler.go
level=info time=2023-05-05T22:17:23Z msg="Sending state change to ECS" taskArn="arn:aws:ecs:us-west-2:039193556298:task/usw2/0b670ab4398f4f138e1bad9293f563a0" taskStatus="RUNNING" taskReason="" taskPullStartedAt="2023-05-05T22:16:44Z" eventType="TaskStateChange" taskKnownSentStatus="RUNNING" taskPullStoppedAt="2023-05-05T22:16:44Z" taskExecutionStoppedAt="0001-01-01T00:00:00Z" containerChange-0="containerName=nonessential containerStatus=STOPPED containerExitCode=0 containerKnownSentStatus=RUNNING containerRuntimeID=9bd88a86abd927421788d5aae9c4ec95b42b16e6d98a5b43940f084b60a1a91d containerIsEssential=false"
```

agent/api/task/task.go

@@ -2592,6 +2592,9 @@ func (task *Task) dockerHostBinds(container *apicontainer.Container) ([]string,
 // It will return a bool indicating if there was a change
 func (task *Task) UpdateStatus() bool {
 	change := task.updateTaskKnownStatus()
+	if change != apitaskstatus.TaskStatusNone {
+		logger.Debug("Task known status change", task.fieldsUnsafe())
+	}
 	// DesiredStatus can change based on a new known status
 	task.UpdateDesiredStatus()
 	return change != apitaskstatus.TaskStatusNone
@@ -2609,11 +2612,7 @@ func (task *Task) UpdateDesiredStatus() {
 // updateTaskDesiredStatusUnsafe determines what status the task should properly be at based on the containers' statuses
 // Invariant: task desired status must be stopped if any essential container is stopped
 func (task *Task) updateTaskDesiredStatusUnsafe() {
-	logger.Debug("Updating task's desired status", logger.Fields{
-		field.TaskID:        task.GetID(),
-		field.KnownStatus:   task.KnownStatusUnsafe.String(),
-		field.DesiredStatus: task.DesiredStatusUnsafe.String(),
-	})
+	logger.Debug("Updating task's desired status", task.fieldsUnsafe())
 
 	// A task's desired status is stopped if any essential container is stopped
 	// Otherwise, the task's desired status is unchanged (typically running, but no need to change)
@@ -2622,13 +2621,8 @@ func (task *Task) updateTaskDesiredStatusUnsafe() {
 			break
 		}
 		if cont.Essential && (cont.KnownTerminal() || cont.DesiredTerminal()) {
-			logger.Info("Essential container stopped; updating task desired status to stopped", logger.Fields{
-				field.TaskID:        task.GetID(),
-				field.Container:     cont.Name,
-				field.KnownStatus:   task.KnownStatusUnsafe.String(),
-				field.DesiredStatus: apitaskstatus.TaskStopped.String(),
-			})
 			task.DesiredStatusUnsafe = apitaskstatus.TaskStopped
+			logger.Info("Essential container stopped; updated task desired status to stopped", task.fieldsUnsafe())
 		}
 	}
 }
@@ -2916,6 +2910,19 @@ func (task *Task) stringUnsafe() string {
 		len(task.Containers), len(task.ENIs))
 }
 
+// fieldsUnsafe returns logger.Fields representing this object
+func (task *Task) fieldsUnsafe() logger.Fields {
+	return logger.Fields{
+		"taskFamily":        task.Family,
+		"taskVersion":       task.Version,
+		"taskArn":           task.Arn,
+		"taskKnownStatus":   task.KnownStatusUnsafe.String(),
+		"taskDesiredStatus": task.DesiredStatusUnsafe.String(),
+		"nContainers":       len(task.Containers),
+		"nENIs":             len(task.ENIs),
+	}
+}
+
 // GetID is used to retrieve the taskID from taskARN
 // Reference: http://docs.aws.amazon.com/general/latest/gr/aws-arns-and-namespaces.html#arn-syntax-ecs
 func (task *Task) GetID() string {

agent/eventhandler/task_handler.go

@@ -184,9 +184,8 @@ func (handler *TaskHandler) startDrainEventsTicker() {
 			// the tasksToContainerStates and tasksToManagedAgentStates maps based on the
 			// task arns of containers and managed agents that haven't been sent to ECS yet.
 			for _, taskEvent := range handler.taskStateChangesToSend() {
-				seelog.Infof(
-					"TaskHandler: Adding a state change event to send batched container/managed agent events: %s",
-					taskEvent.String())
+				logger.Debug("TaskHandler: Adding a state change event to send batched container/managed agent events",
+					taskEvent.ToFields())
 				// Force start the the task state change submission
 				// workflow by calling AddStateChangeEvent method.
 				handler.AddStateChangeEvent(taskEvent, handler.client)