Add the ability for pull requests to be automatically declined by the system if they have had no recent activity.
- the amount of time could be configurable (e.g. N days, N weeks, months, year, ..)
- the configuration could be a project level setting (overridable at the repository level)
- the system could take ownership for the decline action
- the time based decline could override any other factors keeping the pull request open
- changes to the target branch shouldn't count as activity to the pull request
This is potentially useful functionality for both a developer's user experience (less clutter in PR list/dashboard etc., pseudo reminder to either readdress outstanding work or move it to won't do) and also for the system admin (every open pull request is rescoped whenever either the source or target branch changes, so this could mean redundant rescopes if there are many old/not worked on PRs targetting a hot branch like master).