Update toc.yml

Author: dekadays

articles/cost-management-billing/reservations/toc.yml

@@ -38,6 +38,8 @@
       href: /azure/postgresql/single-server/concept-reserved-pricing?toc=/azure/cost-management-billing/reservations/toc.json
     - name: Azure OpenAI
       href: azure-openai.md
+    - name: Azure AI Foundry 
+      href: azure-ai-foundry.md
     - name: Azure SQL Edge
       href: discount-sql-edge.md
     - name: Database for MySQL