Auto-add contributors based on configuration

[flanakin]

Is your feature request related to a problem? Please describe.
I often forget to add people. I want the list to be auto-managed for me. I have a bot doing it today, but that causes a lot of noise unless I add rules to not flag existing contributors. As the repo grows, this will get unmaintainable.

Describe the solution you'd like
I want the bot to monitor my repo and auto-add people based on preconfigured rules.

Describe alternatives you've considered
I'm currently using a separate bot to trigger it.