[Feature Request] Allow filtering feeds by entry author

[mwstobo]

As a user, I'd like to be able to filter some feeds by entry author. Sometimes I only want to read entries posted by a certain person, and I currently don't have a way to do that.

I see that #2269 implemented similar logic for tags, and this would be an extension of that feature.

• I have read this document: https://miniflux.app/opinionated.html#feature-request