Unify all licensed features names to `ai_features`

What does this MR do and why?

All AI features are on one plan: ultimate. But because of the granularity, it's harder to write specs if we change a class that interacts with all of the features (please see MR: !136487 (diffs)).

By using one licensed_feature, nothing changes for our users, but writing tests is simpler.

The downside of this is when one of the features will be downgraded to lower tier: than this plan will work against us.

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