Code Insights: use env context variable for gql insight api on FE
Created by: vovakulikov
Closes https://github.com/sourcegraph/sourcegraph/issues/28513
This PR does a few things
- Changes a variable name to codeInsightsGqlApiEnabled in JSON body of JsContext struct on BE
- Deprecates a setting based experimental feature flag
- Uses
window.context
feature flag (the new one) in code insights main component to switch different API