Sync wiki from 0d20273
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Sync wiki from repo: billing v3.5.9 updates, add Waterfall + Yandex pages - Billing-Integration: v3.5.9, setDebugMode, automatic-acknowledgment note, Product Metadata (v3.4.1+) and Structured Offers (v3.5.7+) sections - Home / Subscriptions / _Sidebar: bring in line with repo wiki/ - Add Multi-Provider-Waterfall and Yandex-Integration pages