dbconsole: add elastic store metric to the overload page

This patch uses the new sperated `elastic-stores` metrics for queing
delay from cockroachdb#123890.

Informs cockroachdb#121572.

Release note (ui change): The `Admission Queueing Delay – Store` chart
now separates elastic (background) work from the regular foreground
work.

pkg/ui/workspaces/db-console/src/views/cluster/containers/nodeGraphs/dashboards/overload.tsx

@@ -193,6 +193,13 @@ export default function (props: GraphDashboardProps) {
               sources={[nid]}
               downsampleMax
             />
+            <Metric
+              key={nid}
+              name="cr.node.admission.wait_durations.elastic-stores-p99"
+              title={"elastic (background) write " + nodeDisplayName(nodeDisplayNameByID, nid)}
+              sources={[nid]}
+              downsampleMax
+            />
           </>
         ))}
       </Axis>