Handle non-happy paths with PR comments / issues opened

[premun]

The PCS code flow is currently implemented to make the happy path work. The code is full of TODOs for when things go wrong and we will resolve these on case by case basis.

When things fail in the PCS, we will need to report that - e.g. post a comment on a PR or open an issue or log a metric which will trigger an alert in Grafana etc.