Filter to only show models and tests that have associated validation results

[appukuttan-shailesh]

We wish to add a filter in the "Configuration Form" where users can specify if only models and tests with validation results are to be displayed.

The GET end-points for models and tests does not contain result related info at the moment. This necessitates us to call the results end-point for each model and test to check if there are associated results.

Proposed solution:
Add a counter in the model and test GET end-points that indicates number of associated results (across all instances of that model/test).