metrics: set sync load latency as P9999 (#56981)

close #56980

Author: hawkingrei

pkg/metrics/grafana/tidb.json

@@ -17251,7 +17251,7 @@
           "targets": [
             {
               "exemplar": true,
-              "expr": "histogram_quantile(0.95, sum(rate(tidb_statistics_sync_load_latency_millis_bucket{k8s_cluster=\"$k8s_cluster\", tidb_cluster=\"$tidb_cluster\", instance=~\"$instance\"}[1m])) by (le))",
+              "expr": "histogram_quantile(0.9999, sum(rate(tidb_statistics_sync_load_latency_millis_bucket{k8s_cluster=\"$k8s_cluster\", tidb_cluster=\"$tidb_cluster\", instance=~\"$instance\"}[1m])) by (le))",
               "format": "time_series",
               "interval": "",
               "intervalFactor": 2,
@@ -17261,7 +17261,7 @@
             },
             {
               "exemplar": true,
-              "expr": "histogram_quantile(0.95, sum(rate(tidb_statistics_read_stats_latency_millis_bucket{k8s_cluster=\"$k8s_cluster\", tidb_cluster=\"$tidb_cluster\", instance=~\"$instance\"}[1m])) by (le))",
+              "expr": "histogram_quantile(0.9999, sum(rate(tidb_statistics_read_stats_latency_millis_bucket{k8s_cluster=\"$k8s_cluster\", tidb_cluster=\"$tidb_cluster\", instance=~\"$instance\"}[1m])) by (le))",
               "format": "time_series",
               "hide": false,
               "interval": "",
@@ -17275,7 +17275,7 @@
           "timeFrom": null,
           "timeRegions": [],
           "timeShift": null,
-          "title": "Sync Load Latency 95",
+          "title": "Sync Load Latency P9999",
           "tooltip": {
             "shared": true,
             "sort": 0,