[BUG]Fork index detector action from transport thread to avoid blocking it

[eirsep]

% curl localhost:9200/_cat/tasks?v | less
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
action                                                     task_id                        parent_task_id                 type      start_time    timestamp running_time ip            node
cluster:admin/opensearch/securityanalytics/detector/write  NS5L3EYoSM2ED7Ivqq1snQ:990205  -                              transport 1706578051254 01:27:31  5.2h         10.212.111.51 5112ba5b511cfd4495
cluster:admin/opensearch/securityanalytics/detector/write  NS5L3EYoSM2ED7Ivqq1snQ:991197  -                              transport 1706578171258 01:29:31  5.2h         10.212.111.51 5112ba5b511cfd4495

[praveensameneni]

Reference PR: #871