telemetry: Use zap.Error() instead of err.Error()

With JSON formatted logs:
```
$ jq 'select(.error) | select(.error | contains("Prometheus"))' tidb.log
{
  "level": "INFO",
  "time": "2023/01/27 10:00:35.554 +01:00",
  "caller": "data_slow_query.go:67",
  "message": "Failed to get Slow Query Stats",
  "error": "[domain:9009]Prometheus address is not set in PD and etcd"
}
{
  "level": "INFO",
  "time": "2023/01/27 10:01:36.223 +01:00",
  "caller": "data_window.go:257",
  "message": "Error exists when getting the SQL Metric.",
  "error": "[domain:9009]Prometheus address is not set in PD and etcd"
}
{
  "level": "INFO",
  "time": "2023/01/27 10:02:36.225 +01:00",
  "caller": "data_window.go:257",
  "message": "Error exists when getting the SQL Metric.",
  "error": "[domain:9009]Prometheus address is not set in PD and etcd"
}
```

telemetry/data_feature_usage.go

@@ -27,6 +27,7 @@ import (
 	"github.com/pingcap/tidb/util/logutil"
 	"github.com/pingcap/tidb/util/sqlexec"
 	"github.com/tikv/client-go/v2/metrics"
+	"go.uber.org/zap"
 )
 
 // emptyClusterIndexUsage is empty ClusterIndexUsage, deprecated.
@@ -61,7 +62,7 @@ func getFeatureUsage(ctx sessionctx.Context) (*featureUsage, error) {
 	var err error
 	usage.NewClusterIndex, usage.ClusterIndex, err = getClusterIndexUsageInfo(ctx)
 	if err != nil {
-		logutil.BgLogger().Info(err.Error())
+		logutil.BgLogger().Info("Failed to get feature usage", zap.Error(err))
 		return nil, err
 	}
 

telemetry/data_slow_query.go

@@ -65,7 +65,7 @@ var (
 func getSlowQueryStats(ctx sessionctx.Context) (*slowQueryStats, error) {
 	slowQueryBucket, err := getSlowQueryBucket(ctx)
 	if err != nil {
-		logutil.BgLogger().Info(err.Error())
+		logutil.BgLogger().Info("Failed to get Slow Query Stats", zap.Error(err))
 		return nil, err
 	}
 

telemetry/data_window.go

@@ -248,7 +248,7 @@ func RotateSubWindow() {
 	err := readSQLMetric(time.Now(), &thisSubWindow.SQLUsage)
 	if err != nil {
 		logutil.BgLogger().Info("Error exists when getting the SQL Metric.",
-			zap.String("error", err.Error()))
+			zap.Error(err))
 	}
 
 	thisSubWindow.SQLUsage.SQLTotal = getSQLSum(&thisSubWindow.SQLUsage.SQLType)