Add Error Metric

[AgeManning]

It would be useful to add a warning and error metric to the global metrics.

This way if an error or warning occurs we increment these counts. Often in Lighthouse, we dont emit logs for discovery and a variety of errors and warnings can go unnoticed.

If we had these in the metrics we could just monitor metrics for discovery to observe if anything is going wrong.
I think it would be good to add the following metrics:

• Error count
• Warning count
• Error Type - Give some string context as to which type of error this is. As the debug logs are not saved and we see a large error/warning count it would be good to provide some context into what these errors are.

[jmcph4]

Error Type - Give some string context as to which type of error this is. As the debug logs are not saved and we see a large error/warning count it would be good to provide some context into what these errors are.

Is the intent here for this to collect the actual error types themselves (i.e., Vec<ErrorKind>) or maintain counters for each type?

[AgeManning]

Upstream users can build their own as was done in lighthouse.