Add observability for webhooks filtered out or with failed filtering

The following discussion from !224355 (merged) should be addressed:

thought: one thing I noticed is that FilterEvaluator.evaluate rescues all StandardError and returns false, which means in case of an error the webhook is silently skipped and there is no WebHookLog entry for the user. While this error path is unlikely to be hit today (since filters can only be set via Rails console manually), it could become a real concern when the API/UI is introduced.

Something to consider for the follow-up is also adding observability (e.g., ErrorTracking.track_exception, metrics).