[15.4] - drop new package requests for Leap where we were not able to find maintainer

[lkocman]

We have directly closed requests to add package to distribution in case that requester did not want to be the maintainer. Let's be bit more polite have a wish-to-be-maintained-in-leap call on factory and see if there are some volunteers

The deadline for the drop should be with entering Beta phase

Current tag that we use is Leap-maintainer-missing https://code.opensuse.org/leap/features/issues?tags=Leap-Maintainer-Missing