Add unbranded emitter to config (#54045)

Author: JoshLove-msft

eng/tsp-client-config.yaml

@@ -3,3 +3,5 @@ supportedEmitters:
     path: eng/azure-typespec-http-client-csharp-emitter-package.json
   - name: "@azure-typespec/http-client-csharp-mgmt"
     path: eng/azure-typespec-http-client-csharp-mgmt-emitter-package.json
+  - name: "@typespec/http-client-csharp"
+    path: eng/http-client-csharp-emitter-package.json