kcoreaddons_add_plugin: add an optional arg to set OUTPUT_NAME
This is needed for KIO, where the kioslaves end up installed as e.g.: /kf5/kio/kio_file.so
being able to set the output name means the "kio" bit doesn't get repeated.
This is needed for KIO, where the kioslaves end up installed as e.g.: /kf5/kio/kio_file.so
being able to set the output name means the "kio" bit doesn't get repeated.