Fix MCP allowlist guidance for Azure API Center registry URL (#61473)

Author: theomonfort

data/reusables/copilot/mcp/azure-api-center-url.md

@@ -1,2 +1,14 @@
 > [!NOTE]
-> If you set up your MCP registry using Azure API Center, enter the base URL for your API Center. Including route suffixes like `/v0.1/servers` will cause the registry to error out.
+> If you set up your MCP registry using Azure API Center, enter the base URL for your API Center, including the workspace path, in the format:
+>
+> ```text
+> https://SERVICE-NAME.data.REGION.azure-apicenter.ms/workspaces/WORKSPACE-NAME
+> ```
+>
+> For example:
+>
+> ```text
+> https://contoso-apic.data.eastus.azure-apicenter.ms/workspaces/default
+> ```
+>
+> Including additional route suffixes like `/v0.1/servers` will cause the registry to error out, because {% data variables.product.prodname_copilot %} appends the MCP v0.1 path automatically.