Add Task Manager for Jira Admin to monitor and manage tasks

Currently, Data Center an executing task can be monitored through a pop-up of a task progress bar from the user who started the task, or using a URL. 

The System Admin has no visibility to view all current running tasks or manage them.  There are support cases where customers indicate tasks are stuck in the 'in progress' state in Task Manager but the "atlassian-jira.log" files indicated the tasks have been completed.  

One example is the migration of project issues when a large number of projects are affected by a workflow change.  The task will have to update many issues in many projects can take days or weeks, see JRASERVER-71742, during the long process we have seen some of the migration tasks getting stuck but the task is completed in the logs.  In the past, we have been using REST API or ScriptRunner to delete the 'stuck' task.  

The customer is on version 9.4.6, and the fix in JRASERVER-66204 "Bulk Operation can get stuck in JIRA Data Center" has no effect on cleaning the 'stuck' tasks.  Therefore, manual validation of the tasks that are completed (using log files) is still required before deleting the tasks.

This enhancement request is to add two functionalities to Jira System Admin:

1. View currently running tasks
2. Allow the Admin to delete a task

The added functionality not only benefits the customer but also for the support team to troubleshoot task-related problems.  Task Manager is an in-memory component, and there is no supported method to access them and view them.