Code Insights: [FE] Remove old settings api code from webapp

Created by: unclejustin

We have a lot of old code to transform data between the settings and GraphQL APIs.

We need to remove this code and update all of the types. I think with will take a good amount of work because there is no way to break this up into smaller chunks (that I can see at this time).

To-do

• https://github.com/sourcegraph/sourcegraph/pull/31670
• https://github.com/sourcegraph/sourcegraph/pull/31799 @vovakulikov
• https://github.com/sourcegraph/sourcegraph/pull/31826
• https://github.com/sourcegraph/sourcegraph/pull/32009 @vovakulikov
• Remove setting-based API insight fields (like insight visibility which doesn't exist anymore in the GQL API)
• Remove setting-based API codebase (implementation class and all related helpers) https://github.com/sourcegraph/sourcegraph/pull/32057