Resolve "API to let extensions know if user is provisioned"

What does this MR do and why?

Adds duoCodeSuggestionsAvailable for a user type in GraphQL to check if code suggestions have been provisioned for a user

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

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Before	After

How to set up and validate locally

1. To check on self-managed, please follow the steps here: !140352 (merged)

2. to check on SaaS, follow the steps here: https://docs.gitlab.com/ee/development/ai_features/index.html#test-saas-only-ai-features-locally

3. Go into http://127.0.0.1:3000/-/graphql-explorer

4. put

   query aiAccess {
     currentUser {
      duoCodeSuggestionsAvailable
     }
   }

5. Observe results.

Related to #437172 (closed)