Add the licensed feature and user message

What does this MR do and why?

Unblock the front end to merge on an AI experiment by providing:

1. What the mutation will return. A user message which will be used to start polling Apollo once this is merged.
2. A method to check the feature flags and licensed features are enabled.

See the architecture here: !117924 (closed)

Issue: https://gitlab.com/gitlab-org/gitlab/-/issues/407739

MR acceptance checklist

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