Include co-author contributors into the "more authors" list

[rkotze]

Summary

Include authors in "more authors" list if they contributed via co-authors metadata only.

Motivation

Only Git authors are listed in "more authors" and you won't find a co-author contributor. Useful to have all author types findable.

Notes

Might be handy for finding co-authored metadata in log:
https://stackoverflow.com/questions/61263083/how-to-query-git-log-for-co-authored-by/61264586#61264586