[FR] Allow analysts to mark an untouched task to not be deleted when closing the case

[dealtwith]

Feature description
Some kind of dontDelete flag or a separate status other than Waiting, inProgress, or Completed -- something that can be assigned to a task so that it won't be deleted if it's untouched when closing a case.

Describe the solution you'd like
^

Additional context
I understand there's a discussion in #1755 about this. To quote @nadouani:

TheHive deletes tasks that have not been started at all, when closing a case. There is no valid reason to keep those tasks.

But having the ability to flag a Waiting task to not get deleted allows Incident Responders to also include a task that are considered to be "Post-incident activities" inside the case. Some examples of tasks that can be categorized as a "Post-incident activities" are "Create a follow-up report" and "Hold a lessons learned meeting" (NIST, SP 800-61 Rev. 2).

These tasks may be considered as "part-of-the-case", but not necessarily something that should be done WHILE case investigation is ongoing.

[dealtwith]

Wrong repo. Closing this. Go to TheHive-Project/TheHive#2287