[3.12] gh-111699: Move smtpd note to dedicated section in What's New Python 3.12 doc (GH-112544) (GH-112552)

Relocate smtpd deprecation notice to it's own section rather than under
'locale' in docs for What's New in Python 3.12 doc
(cherry picked from commit 1ff212debdc094c28928011cff9f4eea8de34d44)

Co-authored-by: Matt Prodani <mp5908@nyu.edu>