No FMN notifications when the submitter is a namespaced username

[knurd]

[This is a follow up to comments in an earlier issue]

I do not get any FMN notifications for copr builds I trigger through a commit to gitlab with a matching copr webhook. To fix this it seems copr would need to resolve the username using FAS an pass that to FMN. For details see abompard's comment at #3099 (comment) and the comments following it.