Load balance @envoyproxy/api-shepherds via RepoKitteh. This will work as follows:

1. An auto_assign attribute will be added to the existing repokitteh.star specs.
2. When a PR is updated, the set of GH users in owners will be computed, call this Owners.
3. We will compute the union of the assigness for the PR and requested reviewers for the PR, call this Assigned.
4. If the intersection of Owners and Assigned is non-empty, there is no need for action.
5. Otherwise, a random member of Owners will be selected and a review requested. They will be nominated in the issue update comment as acting for the specced team.
   This work is currently blocked on Add to github API the ability to list assignees repokitteh/modules#23. CC @itayd