591296 Historical Addon Assignments - Ignore Namespace Path For SM

What does this MR do and why?

We had multiple instances from SM customers complaining about AI Metrics / AI User Metrics after upgrading to 18.7

After discovery calls and debugging. The reason was that addon assignments is set to 0/ in SM yet we send a namespace_path for filtering that can be related to group/project. Causing incosistency and us being unable to match the data (https://gitlab.com/gitlab-com/request-for-help/-/work_items/4063)

This changes addresses this issue till historical addon assignments are removed. This fix will be backported as well for %18.9, %18.8 and %18.7

References

Screenshots or screen recordings

Before	After

How to set up and validate locally

• Run the specs:

ENABLE_SPRING=1 bundle exec rspec ee/spec/finders/gitlab_subscriptions/concerns/historical_add_on_assigned_users_spec.rb

• (Optional) Update CH data to have namespace_path set to 0/, set Gitlab.com? to false. Call the relevant GraphQL queries and see it fetches data correctly

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Related to #591296 (closed)