[FEATURE] Add user name into threadContext header

[Hailong-am]

Is your feature request related to a problem?
There has some long running operations like reindex, split, shrink etc in OpenSearch, we plan to add notification feature when those long running operation complete. For the notification, it's better to have operator info included as well.

What solution would you like?
we want to store operator name into task when it was registered in TransportAction, TaskManager. As core has the logic in place of reading all headers from thread context headers and put it into task, what we need to do is just put the user name into thread context header.

What alternatives have you considered?

• User object has already stored in threadContext, we could pull it from there and put into task. that need to introduce a user concept into core and that only available in plugin only.

Do you have any additional context?
More details about notification could be found in opensearch-project/OpenSearch#5479

[stephen-crawford]

[Triage] Hi @Hailong-am, thank you for taking the time to file this issue. Currently, the Security Plugin has no plans to implement the features you are requesting. However, the new Identity project may be able to incorporate the features you are requesting. You can find more information here.