Workflow auto-nudge

An automated, lightweight comment to keep PRs moving forward.

Each workflow has the option to enable an "auto-nudge". This is a lightweight way to remind both reviewers and authors to continue moving a PR forward towards merge.

The nudge itself is the same as a manual nudge, but it is sent automatically based on recent activity on the PR. The auto-nudge will only be sent one time per PR, and only if there has been no activity on the PR for a specified number of days.