use the feature summary to communicate runtime deps
Test Plan:
- cmake
- prints warning
- can be overridden with CMAKE_DISABLE_FIND_PACKAGE_foo
Reviewers: Plasma, davidedmundson
Reviewed By: Plasma, davidedmundson
Subscribers: davidedmundson, heikobecker, plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D2377