Currently, `TransportGetShutdownStatusAction` is executed in a transport thread, this action can do a substantial amount of work (O(# shards) in some cases) in the transport thread preventing pending transport tasks to make progress and potentially causing cluster instability. This action should be dispatched into a different thread pool to avoid such issues.
x-pack/plugin/shutdown/src/test/java/org/elasticsearch/xpack/shutdown/TransportGetShutdownStatusActionTests.java
var indexRoutingTableBuilder = IndexRoutingTable.builder(index);
        for (var routing : shards) {
            indexRoutingTableBuilder.addShard(routing);
        }
        var indexRoutingTable = indexRoutingTableBuilder.build();
        
        canAllocate.set((r, n, a) -> Decision.NO);
        
        canRemain.set((r, n, a) -> n.nodeId().equals(SHUTTING_DOWN_NODE_ID) ? Decision.NO : Decision.YES);
        RoutingTable.Builder routingTable = RoutingTable.builder();
        routingTable.add(indexRoutingTable);
        ClusterState state = createTestClusterState(
            routingTable.build(),
            List.of(imd),
            SingleNodeShutdownMetadata.Type.REMOVE,
            randomBoolean()
        );
        return TransportGetShutdownStatusAction.shardMigrationStatus(
            state,
            SHUTTING_DOWN_NODE_ID,
            SingleNodeShutdownMetadata.Type.REMOVE,
            true,
            clusterInfoService,
            snapshotsInfoService,
            allocationService,
            allocationDeciders
        );
    }
}