Track individual contributors too

[quic-mathbern]

For now, contribution-tracker is focused on organizations. It would be interesting if one could also specify individuals in the config file in an easy way.

We can already do something like:

org_files:
    John: *
    
org_domains:
    John: john@doe.com

But that is hacky and ugly.

[github-actions]

This issue is stale. Add a nice message, can mention maintainers or maintainer team to draw attention