Notifications: Separate Issue Created from (new) Sub-Task created

I think this issue should be part of resolving [#JRA-9941] new notification type for "Sub-task of issue created" but if it goes faster I would really prefer to have the standalone fix:

We have a notification scheme which informs every developer about new issues in a project. This is nice as it is easy to keep track of new issues or add comments if you know more about it.

But there is a problem: As Issue Created notification also applies to Sub-Tasks the developers get a huge heap of unwanted notification mails.

This is because we use Sub-Tasks as a way a developers might organize their work to document step by step approach. Thus most of the time such sub-tasks are more like private todos than anything interesting to the public.

I suggest to have a separate notification called Sub-Task created which is independent from Issue created.

If resolving JRA-9941 it might still be good to have the two notifications introduced here just in case you want to simulate the old behavior, i. e. getting Sub-Task created mails just as Sub-Task for Issue created (as proposed by JRA-9941).