Add missing properties (fixes microsoft/vscode-remote-release#1961)

extensions/configuration-editing/schemas/attachContainer.schema.json

@@ -18,6 +18,10 @@
 						"type": "integer"
 					}
 				},
+				"settings": {
+					"$ref": "vscode://schemas/settings/machine",
+					"description": "Machine specific settings that should be copied into the container."
+				},
 				"remoteEnv": {
 					"type": "object",
 					"additionalProperties": {