Deprecate alternatives to the hot threads API (#52930)

This commit deprecates various undocumented alternatives to the hot
threads API.

server/src/main/java/org/elasticsearch/rest/action/admin/cluster/RestNodesHotThreadsAction.java

@@ -34,25 +34,67 @@
 
 import java.io.IOException;
 import java.util.List;
+import java.util.Locale;
 
 import static java.util.Arrays.asList;
 import static java.util.Collections.unmodifiableList;
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 
-
 public class RestNodesHotThreadsAction extends BaseRestHandler {
 
+    private static final String formatDeprecatedMessageWithoutNodeID = "[%s] is a deprecated endpoint. " +
+        "Please use [/_nodes/hot_threads] instead.";
+    private static final String formatDeprecatedMessageWithNodeID = "[%s] is a deprecated endpoint. " +
+        "Please use [/_nodes/{nodeId}/hot_threads] instead.";
+    private static final String DEPRECATED_MESSAGE_CLUSTER_NODES_HOT_THREADS = String.format(Locale.ROOT,
+        formatDeprecatedMessageWithoutNodeID,
+        "/_cluster/nodes/hot_threads"
+    );
+    private static final String DEPRECATED_MESSAGE_CLUSTER_NODES_NODEID_HOT_THREADS = String.format(Locale.ROOT,
+        formatDeprecatedMessageWithNodeID,
+        "/_cluster/nodes/{nodeId}/hot_threads"
+    );
+    private static final String DEPRECATED_MESSAGE_CLUSTER_NODES_HOTTHREADS = String.format(Locale.ROOT,
+        formatDeprecatedMessageWithoutNodeID,
+        "/_cluster/nodes/hotthreads"
+    );
+    private static final String DEPRECATED_MESSAGE_CLUSTER_NODES_NODEID_HOTTHREADS = String.format(Locale.ROOT,
+        formatDeprecatedMessageWithNodeID,
+        "/_cluster/nodes/{nodeId}/hotthreads"
+    );
+    private static final String DEPRECATED_MESSAGE_NODES_HOTTHREADS = String.format(Locale.ROOT,
+        formatDeprecatedMessageWithoutNodeID,
+        "/_nodes/hotthreads"
+    );
+    private static final String DEPRECATED_MESSAGE_NODES_NODEID_HOTTHREADS = String.format(Locale.ROOT,
+        formatDeprecatedMessageWithNodeID,
+        "/_nodes/{nodeId}/hotthreads"
+    );
+
+    @Override
+    public List<DeprecatedRoute> deprecatedRoutes() {
+        return unmodifiableList(asList(
+            new DeprecatedRoute(GET, "/_cluster/nodes/hot_threads",
+                    DEPRECATED_MESSAGE_CLUSTER_NODES_HOT_THREADS),
+            new DeprecatedRoute(GET, "/_cluster/nodes/{nodeId}/hot_threads",
+                    DEPRECATED_MESSAGE_CLUSTER_NODES_NODEID_HOT_THREADS),
+            new DeprecatedRoute(GET, "/_cluster/nodes/hotthreads",
+                    DEPRECATED_MESSAGE_CLUSTER_NODES_HOTTHREADS),
+            new DeprecatedRoute(GET, "/_cluster/nodes/{nodeId}/hotthreads",
+                    DEPRECATED_MESSAGE_CLUSTER_NODES_NODEID_HOTTHREADS),
+            new DeprecatedRoute(GET, "/_nodes/hotthreads",
+                    DEPRECATED_MESSAGE_NODES_HOTTHREADS),
+            new DeprecatedRoute(GET, "/_nodes/{nodeId}/hotthreads",
+                    DEPRECATED_MESSAGE_NODES_NODEID_HOTTHREADS)
+        ));
+    }
+
     @Override
     public List<Route> routes() {
         return unmodifiableList(asList(
-            new Route(GET, "/_cluster/nodes/hotthreads"),
-            new Route(GET, "/_cluster/nodes/hot_threads"),
-            new Route(GET, "/_cluster/nodes/{nodeId}/hotthreads"),
-            new Route(GET, "/_cluster/nodes/{nodeId}/hot_threads"),
-            new Route(GET, "/_nodes/hotthreads"),
             new Route(GET, "/_nodes/hot_threads"),
-            new Route(GET, "/_nodes/{nodeId}/hotthreads"),
-            new Route(GET, "/_nodes/{nodeId}/hot_threads")));
+            new Route(GET, "/_nodes/{nodeId}/hot_threads")
+        ));
     }
 
     @Override