Blocks unprovisioned access to product analytics apis

What does this MR do and why?

This allows product analytics apis to restrict product analytics api calls when not provisioned/purchased

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Before	After

How to set up and validate locally

• Set GDK to SaaS simulation and enable product analytics feature flag.

• Create a new group or an already existing group, with ultimate subscription.

• Enable the feature flag product_analytics_billing for the group namespace

  Feature.enable(:product_analytics_billing, namespace, type: :wip)

• Make an api call to the product analytics APIs (/load, /meta, etc.). It should return a 404 Not Found error (If you haven't setup your own PA cluster or purchased PA addon)

• Purchase a PA addon using the api or setup your own cluster

• PA api calls should be unblocked now.

• You can try out the same with GraphQL api projectInitializeProductAnalytics

  mutation {
    projectInitializeProductAnalytics(input: 
      {projectPath: "gitlab-org/my-website"}) {
      project {
        id
        fullPath
      }
      errors
    }
  }
  

Related to #451250