Auto-add contributors based on configuration

**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.