[release plan] abandoned release plan should close the AutoPR it created

-- Or at least add a comment in AutoPR that it is abandoned.

For example, we saw 4 AutoPR from Compute Bulkactions. On investigation we found that 2 of the release plan was already abandoned.
- https://azsdk-releaseplan-dashboard-hveph5aqhhcfhtgu.westus-01.azurewebsites.net/?releaseplan=36132
- https://azsdk-releaseplan-dashboard-hveph5aqhhcfhtgu.westus-01.azurewebsites.net/?releaseplan=35907

As SDK dev usually work on GitHub alone (release is only a thing we throw at agent), and hence not start our workflow from release plan, we'd hope when release plan is abandoned, the related AutoPR would be closed too.