added api key auth docs

.vitepress/config.mts

@@ -36,6 +36,7 @@ export default defineConfig({
           { text: 'Google Sign in without Identity', link: '/dotnet/google-sign-in-without-identity' },
           { text: 'Service Testing', link: '/dotnet/service-testing' },
           { text: 'Controller Testing', link: '/dotnet/controller-testing' },
+          { text: 'API Key Authentication', link: '/dotnet/api-key-auth'}
         ]
       },
       {