Always fetch node usage stats for write load decider

The NodeUsageStats Action will not be unconditionally called
every 30 seconds, regardless of the write load decider being
enabled. It is a lightweight action that fetches stats that
are collected on the node regardless. This supports better
seeing what happens when the write load decider is enabled,
providing a before- (not just after) enablement picture.

ES-12631

Author: DiannaHohensee

server/src/main/java/org/elasticsearch/cluster/InternalClusterInfoService.java

@@ -218,7 +218,7 @@ void execute() {
                 maybeFetchIndicesStats(diskThresholdEnabled || writeLoadConstraintEnabled.atLeastLowThresholdEnabled());
                 maybeFetchNodeStats(diskThresholdEnabled || estimatedHeapThresholdEnabled);
                 maybeFetchNodesEstimatedHeapUsage(estimatedHeapThresholdEnabled);
-                maybeFetchNodesUsageStatsForThreadPools(writeLoadConstraintEnabled);
+                fetchNodesUsageStatsForThreadPools();
             }
         }
 
@@ -257,34 +257,25 @@ private void maybeFetchNodesEstimatedHeapUsage(boolean shouldFetch) {
             }
         }
 
-        private void maybeFetchNodesUsageStatsForThreadPools(WriteLoadDeciderStatus writeLoadConstraintEnabled) {
-            if (writeLoadConstraintEnabled.atLeastLowThresholdEnabled()) {
-                try (var ignored = threadPool.getThreadContext().clearTraceContext()) {
-                    fetchNodesUsageStatsForThreadPools();
-                }
-            } else {
-                logger.trace("skipping collecting shard/node write load estimates from cluster, feature currently disabled");
-                nodeThreadPoolUsageStatsPerNode = Map.of();
-            }
-        }
-
         private void fetchNodesUsageStatsForThreadPools() {
-            nodeUsageStatsForThreadPoolsCollector.collectUsageStats(
-                client,
-                clusterStateSupplier.get(),
-                ActionListener.releaseAfter(new ActionListener<>() {
-                    @Override
-                    public void onResponse(Map<String, NodeUsageStatsForThreadPools> threadPoolStats) {
-                        nodeThreadPoolUsageStatsPerNode = threadPoolStats;
-                    }
+            try (var ignored = threadPool.getThreadContext().clearTraceContext()) {
+                nodeUsageStatsForThreadPoolsCollector.collectUsageStats(
+                    client,
+                    clusterStateSupplier.get(),
+                    ActionListener.releaseAfter(new ActionListener<>() {
+                        @Override
+                        public void onResponse(Map<String, NodeUsageStatsForThreadPools> threadPoolStats) {
+                            nodeThreadPoolUsageStatsPerNode = threadPoolStats;
+                        }
 
-                    @Override
-                    public void onFailure(Exception e) {
-                        logger.warn("failed to fetch thread pool usage estimates for nodes", e);
-                        nodeThreadPoolUsageStatsPerNode = Map.of();
-                    }
-                }, fetchRefs.acquire())
-            );
+                        @Override
+                        public void onFailure(Exception e) {
+                            logger.warn("failed to fetch thread pool usage estimates for nodes", e);
+                            nodeThreadPoolUsageStatsPerNode = Map.of();
+                        }
+                    }, fetchRefs.acquire())
+                );
+            }
         }
 
         private void fetchNodesEstimatedHeapUsage() {