Cherry-pick bot does not add useful reviewers in some situations

In the event that a change is cherry-picked cleanly, but then a child pick somewhere down the line creates merge conflicts, the bot blindly copies reviewers from the immediate parent change. While the original author/owner is added to the attention set, this is ineffective if the author is external to the Qt Company, and the cherry-pick with conflicts is being applied to a tqtc/ restricted repo/branch.

To work around this issue, the bot should parse the commit message and add reviewers according to any non-bot Reviewed By footers.