SDK: Track all feature flag calls

[JonasAlfredsson]

Is your feature request related to a problem? Please describe.

I have been doing some work on the Go SDK and found it weird that the analytics processor only tracked (successful) requests to feature names that are present in the Environment/API. I think it would be interesting to also track requests that are handled by the default flag handler, and those that fail/don't exist.

Describe the solution you'd like

Be able to see statistics for all feature flag requests.

Describe alternatives you've considered

I might perhaps be uninteresting to track failed requests, but then I do believe it would be of value to track requests that go to the default handler at least.

[dabeeeenster]

It would be useful to add meta data to our analytics events to define:

• Handled by an evaluation
• Handled by a default
• Missing