update toc and andd link

Author: bandersmsft

articles/cost-management-billing/reservations/prepare-buy-reservation.md

@@ -85,6 +85,7 @@ You can purchase reservations from Azure portal, APIs, PowerShell, CLI. Read the
 - [Azure Files](../../storage/files/files-reserve-capacity.md?toc=/azure/cost-management-billing/reservations/toc.json)
 - [Azure VMware Solution](../../azure-vmware/reserved-instance.md?toc=/azure/cost-management-billing/reservations/toc.json)
 - [Azure Cosmos DB](../../cosmos-db/cosmos-db-reserved-capacity.md?toc=/azure/cost-management-billing/reservations/toc.json)
+- [Azure OpenAI](open-ai-capacity.md)
 - [Azure SQL Edge](prepay-sql-edge.md)
 - [Databricks](prepay-databricks-reserved-capacity.md)
 - [Data Explorer](/azure/data-explorer/pricing-reserved-capacity?toc=/azure/cost-management-billing/reservations/toc.json)

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

@@ -32,6 +32,8 @@
       href: /azure/cosmos-db/postgresql/resources-pricing?toc=/azure/cost-management-billing/reservations/toc.json
     - name: Azure Database for PostgreSQL
       href: /azure/postgresql/single-server/concept-reserved-pricing?toc=/azure/cost-management-billing/reservations/toc.json
+    - name: Azure OpenAI
+      href: open-ai-capacity.md
     - name: Azure SQL Edge
       href: discount-sql-edge.md
     - name: Database for MySQL