Lazy compute description in ReplicationRequest.createTask (elastic#117783) (elastic#117804)

These can at times be quite long strings, no need to materialize
unless requested. This is showing up as allocating needless heap of
O(GB) in some benchmarks during indexing needlessly.

Author: original-brownbear

server/src/main/java/org/elasticsearch/action/support/replication/ReplicationRequest.java

@@ -210,7 +210,12 @@ public void writeThin(StreamOutput out) throws IOException {
 
     @Override
     public Task createTask(long id, String type, String action, TaskId parentTaskId, Map<String, String> headers) {
-        return new ReplicationTask(id, type, action, getDescription(), parentTaskId, headers);
+        return new ReplicationTask(id, type, action, "", parentTaskId, headers) {
+            @Override
+            public String getDescription() {
+                return ReplicationRequest.this.getDescription();
+            }
+        };
     }
 
     @Override