Refactor how to record feast metrics.

[ariefrahmansyah]

Which issue(s) this PR fixes:

Fixes not able to log NULL feature status if user didn't specify default value.

Checklist

• [ ] Added unit test, integration, and/or e2e tests
• [ ] Tested locally
• [ ] Updated documentation
• [ ] Update Swagger spec if the PR introduce API changes
• [ ] Regenerated Golang and Python client if the PR introduce API changes