add configurable to skip thanking specific contributors

[JeanMertz]

As a core contributor, it's a bit weird to be constantly thanked for your work 😅.

An easy fix is to add a configurable ignore_contributors that takes an array of email addresses, which are then excluded from the list of contributors printed in the release notes.

[jcgruenhage]

This can be solved by modifying the template. I think modifying the template instead would make more sense, as adding it into jilu itself feels like feature creep.