Code Insights: Add series color setting to the backend insight
Created by: vovakulikov
Closes https://github.com/sourcegraph/sourcegraph/issues/23205
Context
At the moment our insight GQL API handler doesn't return information about data series color (in fact that returns only query label and points). But we already have this information in the settings cascade which is available for the code insights chart. This PR reads information from the settings cascade and passes it to the backend insight handler in order to build chart content with series (lines) colors.