MM-58281 Allow client metrics to be floats and round timestamps (#27027)

* MM-58281 Allow client metrics to be floats and round timestamps

* MM-58281 Fix report version

* Ensure reports can contain a single timestamp

* Round timestamps in unit tests

server/public/model/metrics.go

@@ -35,7 +35,7 @@ var (
 
 type MetricSample struct {
 	Metric    MetricType        `json:"metric"`
-	Value     int64             `json:"value"`
+	Value     float64           `json:"value"`
 	Timestamp int64             `json:"timestamp,omitempty"`
 	Labels    map[string]string `json:"labels,omitempty"`
 }
@@ -65,7 +65,7 @@ func (r *PerformanceReport) IsValid() error {
 		return fmt.Errorf("report version is not supported: server version: %s, report version: %s", performanceReportVersion.String(), r.Version)
 	}
 
-	if r.Start >= r.End {
+	if r.Start > r.End {
 		return fmt.Errorf("report timestamps are erroneous")
 	}