### Description

From the nodes stats API, we should extract the `thread_pool` stats into their own endpoint. This endpoint can then be non-node-centric, and present a global view of the number of completed, rejected, and failed operations for each of the threadpools in the system.
server/src/test/java/org/elasticsearch/action/admin/cluster/node/stats/NodeStatsTests.java
.getClusterStateUpdateStats();
                        assertEquals(
                            clusterStateUpdateStats.getUnchangedTaskCount(),
                            deserializedClusterStateUpdateStats.getUnchangedTaskCount()
                        );
                        assertEquals(
                            clusterStateUpdateStats.getPublicationSuccessCount(),
                            deserializedClusterStateUpdateStats.getPublicationSuccessCount()
                        );
                        assertEquals(
                            clusterStateUpdateStats.getPublicationFailureCount(),
                            deserializedClusterStateUpdateStats.getPublicationFailureCount()
                        );
                        assertEquals(
                            clusterStateUpdateStats.getUnchangedComputationElapsedMillis(),
                            deserializedClusterStateUpdateStats.getUnchangedComputationElapsedMillis()
                        );
                        assertEquals(
                            clusterStateUpdateStats.getUnchangedNotificationElapsedMillis(),
                            deserializedClusterStateUpdateStats.getUnchangedNotificationElapsedMillis()
                        );
                        assertEquals(
                            clusterStateUpdateStats.getSuccessfulComputationElapsedMillis(),
                            deserializedClusterStateUpdateStats.getSuccessfulComputationElapsedMillis()
                        );
                        assertEquals(
                            clusterStateUpdateStats.getSuccessfulPublicationElapsedMillis(),
                            deserializedClusterStateUpdateStats.getSuccessfulPublicationElapsedMillis()
                        );
                        assertEquals(