[spanneradapter] Add Methods to Update Channel Health #1875
Description
In the lib/gcpspanner/spanneradapters layer, add a new method to the Notification Channel adapter (e.g., UpdateChannelHealthStatus). This method will be called by the WebhookWorker to update the NotificationChannelState table with the latest delivery status, incrementing the ConsecutiveFailures count on a failure. This must include unit tests.