Check the state of an automated PR and report it in pipeline status

[squaremo]

When a promotion creates an automated PR, there's the possibility that the PR will be closed without merging. This represents that pipeline run being abandoned; it will not make progress without some human intervention (someone reopening the PR!). So, if a pipeline is waiting on promotion PR, it should check the status of that PR and reflect it in the pipeline status.

This should be done in concert with displaying this state in the pipeline UI, so we know it's fit for that purpose.