[FSSDK-9128] fix: Handle ODP INVALID_IDENTIFIER_EXCEPTION code

[mikechu-optimizely]

Summary

Support a new format for ODP InvalidIdentifierException (when SDK fetches segments with a non-registered userId).

       "extensions": {
            "code": "INVALID_IDENTIFIER_EXCEPTION",
            "classification": "DataFetchingException"
       }

Test plan

• Added unit tests to cover the new response format.
• Existing unit tests should pass
• FSC should continue to pass

Issues

• FSSDK-9128

[jaeopt]

I do not see a logic change to provide proper error message for INVALID_IDENTIFIER_EXCEPTION. Can you check again?

[jaeopt]

Looks good!
The error "code" is optional. Can you check if we have a test case without code?

[jaeopt]

LGTM