R1:109452707241

Allow Herald to trigger audits for users or projects

Summary:
Allows you to write a commit rule that triggers an audit by a user (personal
rules) or a project (global rules).

Mostly this is trying to make auditing more lightweight and accessible in
environments where setting up Owners packages doesn't make sense.

For instance, Disqus wants a rule like "trigger an audit for everything that
didn't have a Differential revision". While not necessarily scalable, this is a
perfectly reasonable rule for a…