Report telemetry for unexpected events in the property page back end

We should collect and report telemetry for unexpected events in the property page back end implementation. E.g.:

- Querying for a specific page that doesn't exist
- Querying for a specific property that doesn't exist
- Attempting to set a property that doesn't exist

In general, anywhere we look for a specific entity (page, property, configuration, etc.) and it isn't found is a candidate for a telemetry event. While it shouldn't be possible for these things to happen but we are unlikely to encounter an exception if they do; reporting a telemetry event is better then silently dropping the request.