Fix "Change type" when subepics feature is not available

What does this MR do and why?

Fix "Change type" when subepics feature is not available (#608197 (closed))

When the subepics feature is not available, the "Change type" modal does not let you change a work item to a non-epic type when it has a parent. The warning message should only show when trying to promote the work item to an epic without the subepics feature.

Only tasks can have a parent issue, so if a task has a parent issue we show a warning when trying to change its type to anything issue-adjacent

Changelog: fixed

References

• #608197 (closed)

Screenshots or screen recordings

When subepics feature is available	When subepics feature is not available

How to set up and validate locally

1. Go to an issue, add a parent epic, try to change type to an epic. This should work when subepics are available, and not work when subepics are not available

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Related to #608197 (closed)