Diagnostic logs for task runs

**What is the problem you're trying to solve**

I sometimes have failing task runs and I don't have any way to monitor for it. There are no metrics and no diagnostic log events.

**Describe the solution you'd like**

In addition to the existing `ContainerRegistryLoginEvents` and `ContainerRegistryRepositoryEvents` diagnostic log event types, I would like a `ContainerRegistryTaskEvents` log type.

Metrics would be great also. `TotalTaskRunCount` and `SuccessfulTaskRunCount` for example.

**Additional context**

Start by locating the existing ContainerRegistryLoginEvents and ContainerRegistryRepositoryEvents diagnostic log event types and the task-run monitoring implementation. Trace how diagnostic events and metrics are defined, then determine the project’s requirements for ContainerRegistryTaskEvents, TotalTaskRunCount, and SuccessfulTaskRunCount; done means task runs expose the requested diagnostic logs and metrics.

Written by the indexing model from the issue text.