Sub-tasks can be created under Epic

Issue Summary

Scenario 1:

When converting an issue linked to an Epic to a sub-task, if you set the parent to be the Epic, this will allow users to add sub-tasks to Epics directly.

Steps to Reproduce

1. Create a Jira Software project
2. Create an Epic and some stories
3. Make the stories children of the Epic
4. Access one of the stories and convert it to a sub-task
5. In the select parent step, add the issue key of the Epic

Scenario 2:

When converting an Issue with subtasks to an Epic, the subtasks are shown in the Epic and allows users to create new subtasks.

Steps to Reproduce

1. Create a Story and some subtasks in it
2. Convert Story to Epic

Expected Results

Jira blocks the user to move forward and warns the user that an Epic shouldn't have a sub-task

Actual Results

Jira allows the Epic to be the sub-tasks' parent and this enables the view to add more sub-tasks to the Epic

Workaround

Currently, there is no known workaround for this behavior. A workaround will be added here when available