Better instrument incoming webhooks via logging

[jldec]

It would be helpful to validate from our logs that webhook events are being received from specific repositories.
This would allow us to debug issues lie #7648 more easily.

The log data should include the repo, and commit sha for webhook pushes from GitHub.

[jldec]

If we don't have a way to do this already, it would be good to keep track of when the last webhook was received, to show it later in the UI. see #7010

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.