MAINTAINERS: add hung-task detector section

The hung-task detector is missing in MAINTAINERS.  While it's been quiet
recently, I'm actively working on it and volunteering to review patches. 
Adding this section will make it easier for contributors to know who to
contact.

Link: https://lkml.kernel.org/r/20250513052234.46463-1-lance.yang@linux.dev


Signed-off-by: Lance Yang <lance.yang@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>