proposal: Add an white list of users

[alexfauquette]

I would like to do the following:

When the PR's author is a maintainer, it's assigned to the author.
When the PR's author is a community member, I assign it to a maintainer that will help with the review process.

The idea would be to add a white list (containing maintainers' username) such that assigning maintainer PR to themself is automatic, but community members are not.

This would allow to search in PRs "assigned to nobody" and see if their is some PR opened by the community with no one assigned to it.

[srl295]

What happens currently when it's a community member? I'd think it wouldn't be possible to assign a PR to someone who isn't a contributor. Does the action just error?
EDIT No, it's possible to assign a PR to a non-contributor, and this is what happens with the workflow (or manually).

A good improvement to this workflow would be to not assign non-contributor members, but to leave it unassigned. I'd rather not have to maintain this list.