`cubi-tk sodar add-ped` does not write metadata to index when used to update existing entires

[Nicolai-vKuegelgen]

Describe the bug
cubi-tk sodar add-ped can be used to add new samples or update existing ones with the same identifiers.
When used to update samples (i.e. with new metadata), static information (i.e. --library-kit) is not written to the index samples of families with multiple members.

To Reproduce
Steps to reproduce the behavior:

1. use cubi-tk sodar add-ped to update existing trio with new meta information (i.e. --library-kit), that wasn't present before
2. Index will NOT be updated

Expected behavior
Index should also be updated, when new information is given.