insights: customer-facing docs for new API

Created by: Joelkw

Now that we have a graphQL API, we should document it so that users can obtain the full benefits.

We know some customers want to create insights with the API, and others want to export the data via the API.

Docs

• Create a "Managing Code Insights with the API" docs page – can reference the Search Contexts API Docs Page
  • Include a section on "Creating a Code Insight"
  • Include a section on "Read a single Code Insight"
  • Include a section on "List available Code Insights"
• Add this page to the references section of the main docs page