Add KI18n as a find_package target and add to public link list
Due to this change frameworks/kparts@e8cdcc75 I've added KI18n as a direct dependency and added it to the public library link list.
Build error was:
In file included from /builddir/build/BUILD/knotes-6ff27be/src/kontactplugin/knotes_plugin.cpp:9:
/builddir/build/BUILD/knotes-6ff27be/src/apps/knotes_options.h:8:10: fatal error: KLocalizedString: No such file or directory
8 | #include <KLocalizedString>
| ^~~~~~~~~~~~~~~~~~
compilation terminated.