add a scope for filteirng to just complete ratings

[epugh]

Description

when exporting ratings, we don't want to export ratings that, for whatever reason, don't actually have a value! If you watn to export all the docs for a query, regardless of if rated or not, that is what exporting a snapshot does for you!

Motivation and Context

Issue #265 with RRE.

How Has This Been Tested?

unit test, and I have a case in prod to test.

Screenshots or GIFs (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• [] Improvement (non-breaking change which improves existing functionality)
• [] New feature (non-breaking change which adds new functionality)
• [] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [] My code follows the code style of this project.
• [] My change requires a change to the documentation.
• [] I have updated the documentation accordingly.
• [] I have read the CONTRIBUTING document.
• [] I have added tests to cover my changes.
• [] All new and existing tests passed.