feat(core): Add optional Error-Output (#7460)

Add an additional optional error output to which all items get sent that
could not be processed.
![Screenshot from 2023-10-18
17-29-15](https://github.com/n8n-io/n8n/assets/6249596/e9732807-ab2b-4662-a5f6-bdff24f7ad55)

Github issue / Community forum post (link here to close automatically):
https://community.n8n.io/t/error-connector-for-nodes/3094

https://community.n8n.io/t/error-handling-at-node-level-detect-node-execution-status/26791

---------

Co-authored-by: OlegIvaniv <me@olegivaniv.com>

packages/nodes-base/nodes/Code/Code.node.ts

@@ -160,7 +160,12 @@ export class Code implements INodeType {
 				result = await sandbox.runCodeEachItem();
 			} catch (error) {
 				if (!this.continueOnFail()) throw error;
-				returnData.push({ json: { error: error.message } });
+				returnData.push({
+					json: { error: error.message },
+					pairedItem: {
+						item: index,
+					},
+				});
 			}
 
 			if (result) {

packages/nodes-base/nodes/Code/Sandbox.ts

@@ -16,7 +16,7 @@ export interface SandboxContext extends IWorkflowDataProxyData {
 	helpers: IExecuteFunctions['helpers'];
 }
 
-export const REQUIRED_N8N_ITEM_KEYS = new Set(['json', 'binary', 'pairedItem']);
+export const REQUIRED_N8N_ITEM_KEYS = new Set(['json', 'binary', 'pairedItem', 'error']);
 
 export function getSandboxContext(this: IExecuteFunctions, index: number): SandboxContext {
 	return {