Code Insights: Migrate insight integration test to GQL API
Created by: vovakulikov
Related to https://github.com/sourcegraph/sourcegraph/issues/31412
Context
Prior to this PR we run our web app with old setting based API hence we didn't run any integration test over new GQL API. This PR simply migrates our integration test for new GQL API and cleans up our mock and fixtures objects.
Test plan
- Make sure that all integration test work properly without regressions