Fix the "Dropped Requests" panel of Kubernetes API Server Details

This panel was not showing any data in different Kubernetes versions for 2
reasons:

- apiserver_dropped_requests_total was removed from the allowlist, see
  gardener#3502. This means that this panel was not showing any data in any
  Kubernetes version.

- apiserver_dropped_requests_total is deprecated in 1.24 and removed in
  1.25. So in Kubernetes clusters >= 1.25, this panel would have been empty
  for this reason as well.

The replacement metric `apiserver_request_terminations_total`, is already
allowlisted and available since Kubernetes v1.17, so we can simply use
that for a semantically similar query.

Co-authored-by: Istvan Zoltan Ballok <[email protected]>
Co-authored-by: Jeremy Rickards <[email protected]>

charts/seed-monitoring/charts/grafana/dashboards/owners/kubernetes-api-server-details.json

@@ -902,13 +902,17 @@
       "hiddenSeries": false,
       "id": 55,
       "legend": {
+        "alignAsTable": true,
         "avg": false,
         "current": false,
-        "max": false,
+        "max": true,
         "min": false,
+        "rightSide": true,
         "show": true,
+        "sort": "max",
+        "sortDesc": true,
         "total": false,
-        "values": false
+        "values": true
       },
       "lines": true,
       "linewidth": 1,
@@ -927,9 +931,11 @@
       "steppedLine": false,
       "targets": [
         {
-          "expr": "sum(rate(apiserver_dropped_requests_total[$rate])) by (requestKind)",
-          "legendFormat": "{{ requestKind }}",
+          "exemplar": true,
+          "expr": "sum(rate(apiserver_request_terminations_total{code=\"429\"}[$__rate_interval])) by (verb, group, version, resource, subresource)",
+          "hide": false,
           "interval": "",
+          "legendFormat": "{{verb}} {{group}}/{{version}}/{{resource}} {{subresource}}",
           "refId": "A"
         }
       ],
@@ -939,7 +945,7 @@
       "timeShift": null,
       "title": "Dropped Requests",
       "tooltip": {
-        "shared": true,
+        "shared": false,
         "sort": 0,
         "value_type": "individual"
       },