Add YAML schema setting for pipeline yamls (#23632)

.vscode/settings.json

@@ -136,5 +136,8 @@
 	],
 	"application.experimental.rendererProfiling": true,
 	"editor.experimental.asyncTokenization": true,
-	"editor.experimental.asyncTokenizationVerification": true
+	"editor.experimental.asyncTokenizationVerification": true,
+	"yaml.schemas": {
+		"https://raw.githubusercontent.com/microsoft/azure-pipelines-vscode/master/service-schema.json": "build/azure-pipelines/**/*.yml"
+	}
 }