Update table of contents

Author: evachen96

articles/healthcare-apis/fhir/toc.yml

@@ -31,10 +31,12 @@ items:
           href: fhir-service-bicep.md
         - name: Using ARM template
           href: fhir-service-resource-manager-template.md
-    - name: Use Azure AD B2C for an identity provider
-      href: azure-ad-b2c-setup.md
+    - name: Use Microsoft Entra External ID for an identity provider
+      href: azure-entra-external-id-setup.md
       expanded: true
       items: 
+        - name: Use Azure AD B2C for an identity provider
+          href: azure-ad-b2c-overview.md
         - name: Configure multiple service identity providers
           href: configure-identity-providers.md
         - name: Troubleshoot identity provider configuration