Create a Skill for closing obsolete issues #9800

This skill should guide an agent through scraping the issue backlog for issues that we can close (already fixed, obsolete, stale, etc.)

Sample prompt for this task:

I want to find old outdated issues in the flutter/devtools repo that we can close. It could be that we already fixed them, or that they are stale or obsolete. Use gh to look up the oldest issues labeled bug. Investigate and compare with the current state of the project. Search until you find 5 to close. Provide me a summary for each, with references to other PRs or issues to explain why they can be closed.