**Elasticsearch version** (`bin/elasticsearch --version`): 7.16 (earlier too), 8.0, 8.1

**Description of the problem including expected versus actual behavior**:
Currently, the rollover requests are not cancellable, irrespective of the underlying incoming HTTP channel being closed (eg. by a proxy). This could result in clients receiving `504` and retrying the rollovers, resulting in multiple rollover operations being processed (some products issue rollovers without specifying conditions, so this could translate in multiple subsequent rollovers being executed).

This proposes using the `RestCancellableNodeClient` infrastructure for the rollover API, such that elasticsearch can react to the incoming HTTP connection being closed by cancelling the rollover operation.

server/src/main/java/org/elasticsearch/action/admin/indices/rollover/TransportRolloverAction.java
false
                );
                logger.trace("rollover result [{}]", rolloverResult);
                
                
                
                
                
                sourceIndex.set(rolloverResult.sourceIndexName());
                rolloverIndex.set(rolloverResult.rolloverIndexName());
                
                return rolloverResult.clusterState();
            } else {
                
                
                
                return currentState;
            }
        }
        @Override
        public void onFailure(Exception e) {
            listener.onFailure(e);
        }
        @Override
        public void clusterStateProcessed(ClusterState oldState, ClusterState newState) {
            
            
            if (clusterStateProcessed) {
                assert sourceIndex.get() != null : "source index missing on successful rollover";
                assert rolloverIndex.get() != null : "rollover index missing on successful rollover";