The new Parent field allows subtasks to be added to Epics

Issue Summary

Back in 2019, with the permanent change to the new issue view, the ability to create subtasks within Epics was removed to keep the consistency of the hierarchy Epic > Task > Subtask.
With the new parent field update, users can select Epics from within the subtasks and they expect to have the interface to add subtasks directly from within the Epic back

Steps to Reproduce

1. Create a subtask within a normal issue
2. Edit the subtask's parent field
3. Epics are shown as options to be parent issues

Expected Results

Epics should not appear in the list of parents for subtasks

Actual Results

Epics appear in the list if the issue key is typed

Workaround

N/A