net/kf6-kmime: Add new port

Library for handling MIME data.

This library is going to replace KDE PIM mime (net/kmime).
Do not connect it to the Uses/kde.mk yet.

WWW: https://invent.kde.org/frameworks/kmime
(cherry picked from commit 25b5b2e6bc79fd7a05900e61c9de40ed18efcf9e)