Cloudwatch: Use generic null-insertion mechanism (#43507) (#45204)

* Cloudwatch: Fix nil values for a period gap in metrics

* Use fields periods for intervals

(cherry picked from commit 5edcc2e795)

Co-authored-by: Shirley <4163034+fridgepoet@users.noreply.github.com>

pkg/tsdb/cloudwatch/response_parser.go

@@ -162,13 +162,6 @@ func buildDataFrames(startTime time.Time, endTime time.Time, aggregatedResponse
 		timestamps := []*time.Time{}
 		points := []*float64{}
 		for j, t := range metric.Timestamps {
-			if j > 0 {
-				expectedTimestamp := metric.Timestamps[j-1].Add(time.Duration(query.Period) * time.Second)
-				if expectedTimestamp.Before(*t) {
-					timestamps = append(timestamps, &expectedTimestamp)
-					points = append(points, nil)
-				}
-			}
 			val := metric.Values[j]
 			timestamps = append(timestamps, t)
 			points = append(points, val)