feat: use modifier for topk to improve dashboard performance

[rahulguptajss]

Below is the summary of changes

1. Updated topk to use a modifier, leaving some complex queries unchanged.
2. Fixed variable mapping in Prometheus.
3. Corrected topk text in several places.
4. Decided not to change the custom "All" value to .* in this PR after considering the potential impact on cases where a dropdown filter is dependent on a previous filter query. There may be instances where the dropdown is empty, but "All" is still passed, which could lead to incorrect results, especially in the case of flexgroup. We shall handle it in seperate PR.

Below are the pending topk queries which are using hidden vars:

dashboard=cmode/cdot.json path=panels[1].targets[0] use old topk. expr=topk($TopResources, volume_read_data{datacenter=~"$Datacenter",cluster=~"$Cluster",svm=~"$SVM",volume=~"$TopVolumeAvgThroughput"})+topk($TopResources, volume_write_data{datacenter=~"$Datacenter",cluster=~"$Cluster",svm=~"$SVM",volume=~"$TopVolumeAvgThroughput"})
dashboard=cmode/cluster.json path=panels[11].targets[0] use old topk. expr=topk($TopResources, sum(node_volume_avg_latency{datacenter=~"$Datacenter",cluster=~"$Cluster", node=~"$TopVolumeAvgLatency"}) by (node))
dashboard=cmode/cluster.json path=panels[12].targets[0] use old topk. expr=topk($TopResources, sum(node_volume_read_data{datacenter=~"$Datacenter",cluster=~"$Cluster", node=~"$TopVolumeTotalData"}) by (node) + sum(node_volume_write_data{datacenter=~"$Datacenter",cluster=~"$Cluster", node=~"$TopVolumeTotalData"}) by(node))
dashboard=cmode/cluster.json path=panels[13].targets[0] use old topk. expr=topk($TopResources, sum by (node)(node_volume_total_ops{datacenter=~"$Datacenter",cluster=~"$Cluster", node=~"$TopVolumeTotalOps"}))
dashboard=cmode/external_service_op.json path=panels[2].targets[0] use old topk. expr=topk($TopResources, avg by (operation, service_name, svm, cluster) (external_service_op_request_latency{datacenter=~"$Datacenter",cluster=~"$Cluster",svm=~"$SVM",service_name=~"$ServiceName",operation=~"$Operation",key=~"$TopRequestLatency"}))
dashboard=cmode/external_service_op.json path=panels[4].targets[0] use old topk. expr=topk($TopResources, sum by (operation, service_name, svm, cluster) (external_service_op_num_not_found_responses{datacenter=~"$Datacenter",cluster=~"$Cluster",svm=~"$SVM",service_name=~"$ServiceName",operation=~"$Operation",key=~"$TopNotFoundResponse"}))
dashboard=cmode/external_service_op.json path=panels[5].targets[0] use old topk. expr=topk($TopResources, sum by (operation, service_name, svm, cluster) (external_service_op_num_request_failures{datacenter=~"$Datacenter",cluster=~"$Cluster",svm=~"$SVM",service_name=~"$ServiceName",operation=~"$Operation",key=~"$TopRequestFailed"}))
dashboard=cmode/external_service_op.json path=panels[6].targets[0] use old topk. expr=topk($TopResources, sum by (operation, service_name, svm, cluster) (external_service_op_num_requests_sent{datacenter=~"$Datacenter",cluster=~"$Cluster",svm=~"$SVM",service_name=~"$ServiceName",operation=~"$Operation",key=~"$TopRequestSent"}))
dashboard=cmode/external_service_op.json path=panels[7].targets[0] use old topk. expr=topk($TopResources, sum by (operation, service_name, svm, cluster) (external_service_op_num_responses_received{datacenter=~"$Datacenter",cluster=~"$Cluster",svm=~"$SVM",service_name=~"$ServiceName",operation=~"$Operation",key=~"$TopRequestReceived"}))
dashboard=cmode/external_service_op.json path=panels[8].targets[0] use old topk. expr=topk($TopResources, sum by (operation, service_name, svm, cluster) (external_service_op_num_successful_responses{datacenter=~"$Datacenter",cluster=~"$Cluster",svm=~"$SVM",service_name=~"$ServiceName",operation=~"$Operation",key=~"$TopSuccessResponse"}))
dashboard=cmode/external_service_op.json path=panels[9].targets[0] use old topk. expr=topk($TopResources, sum by (operation, service_name, svm, cluster) (external_service_op_num_timeouts{datacenter=~"$Datacenter",cluster=~"$Cluster",svm=~"$SVM",service_name=~"$ServiceName",operation=~"$Operation",key=~"$TopTimeout"}))
dashboard=cmode/flexgroup.json path=panels[3].targets[0] use old topk. expr=topk($TopResources, volume_read_data{datacenter=~"$Datacenter",cluster=~"$Cluster",aggr=~"$Aggregate",volume=~"$TopVolumeAvgThroughput"})+topk($TopResources, volume_write_data{datacenter=~"$Datacenter",cluster=~"$Cluster",aggr=~"$Aggregate",volume=~"$TopVolumeAvgThroughput"})
dashboard=cmode/node.json path=panels[2].targets[0] use old topk. expr=topk($TopResources, nic_rx_bytes+nic_tx_bytes{datacenter=~"$Datacenter",cluster=~"$Cluster",node=~"$Node",nic=~"$TopNicXPut"})
dashboard=cmode/node.json path=panels[3].targets[0] use old topk. expr=topk($TopResources, fcp_read_data+fcp_write_data+fcp_nvmf_read_data+fcp_nvmf_write_data{datacenter=~"$Datacenter",cluster=~"$Cluster",node=~"$Node",port=~"$TopFCUtilXPut"})
dashboard=cmode/volume.json path=panels[5].targets[0] use old topk. expr=topk($TopResources, volume_read_data{datacenter=~"$Datacenter",cluster=~"$Cluster",svm=~"$SVM",volume=~"$TopVolumeAvgThroughput"})+topk($TopResources, volume_write_data{datacenter=~"$Datacenter",cluster=~"$Cluster",svm=~"$SVM",volume=~"$TopVolumeAvgThroughput"})
dashboard=storagegrid/overview.json path=panels[0].targets[0] use old topk. expr=topk($TopResources, avg by(cluster,tenant,datacenter)(storagegrid_tenant_usage_data_bytes{datacenter=~"$Datacenter",cluster=~"$Cluster",tenant=~"$TopTenantUsageBytes"}))
dashboard=storagegrid/overview.json path=panels[1].targets[0] use old topk. expr=topk($TopResources,storagegrid_node_cpu_utilization_percentage{datacenter=~"$Datacenter",cluster=~"$Cluster",node=~"$TopNodeByCPU"})

[cgrinds]

I think we can reuse the map with something like this:

// Check if this metric is in the allowedSuffix map and has a matching unit
if slices.Contains(allowedSuffix[metric], unit) {
  continue
}

[cgrinds]

Since the query does not require whitespace, probably safer to go with this check to reduce false positives

noWhitespace := strings.ReplaceAll(expr.expr, " ", "")
if strings.Contains(noWhitespace, "$__range@end()") {
hasRange = true
}