Cherry-Pick bot should add a user to the attention set with access to a tqtc/ change

At present, if a public change merges and cherry-picks to tqtc/* branches, the original author cannot be added to the attention set of the cherry-pick if necessary (typically due to conflicts).

The cherry-pick bot should determine eligibility of the original author to be added, and then fall back to the original approver if possible with a final fallback to just copying change reviewers.