Tweak behavior of superseding score sets for users without permissions

[bencap]

A superseding score set should only count as superseding if a user has view+ permissions on it. Otherwise, they should still see the most up to date score set which they have permissions for.

See: https://github.com/search?q=repo%3AVariantEffect%2Fmavedb-api%20~ScoreSet.superseding&type=code

[EstelleDa]

I'll need more time to think about how to adjust the searching score set function when I'm back. The original requirement is not showing superseded score sets. However, the current codes don't handle a case where a superseding score set has not been published yet.