feat: External Secrets storage for credentials (#6477)

Github issue / Community forum post (link here to close automatically):

---------

Co-authored-by: Romain Minaud <romain.minaud@gmail.com>
Co-authored-by: Valya Bullions <valya@n8n.io>
Co-authored-by: Csaba Tuncsik <csaba@n8n.io>
Co-authored-by: Giulio Andreini <g.andreini@gmail.com>
Co-authored-by: Omar Ajoue <krynble@gmail.com>

packages/core/src/NodeExecuteFunctions.ts

@@ -136,6 +136,7 @@ import {
 	setAllWorkflowExecutionMetadata,
 	setWorkflowExecutionMetadata,
 } from './WorkflowExecutionMetadata';
+import { getSecretsProxy } from './Secrets';
 import { getUserN8nFolderPath } from './UserSettings';
 
 axios.defaults.timeout = 300000;
@@ -1683,6 +1684,7 @@ export function getAdditionalKeys(
 	additionalData: IWorkflowExecuteAdditionalData,
 	mode: WorkflowExecuteMode,
 	runExecutionData: IRunExecutionData | null,
+	options?: { secretsEnabled?: boolean },
 ): IWorkflowDataProxyAdditionalKeys {
 	const executionId = additionalData.executionId || PLACEHOLDER_EMPTY_EXECUTION_ID;
 	const resumeUrl = `${additionalData.webhookWaitingBaseUrl}/${executionId}`;
@@ -1723,6 +1725,7 @@ export function getAdditionalKeys(
 				: undefined,
 		},
 		$vars: additionalData.variables,
+		$secrets: options?.secretsEnabled ? getSecretsProxy(additionalData) : undefined,
 
 		// deprecated
 		$executionId: executionId,
@@ -1858,6 +1861,7 @@ export async function getCredentials(
 	// }
 
 	const decryptedDataObject = await additionalData.credentialsHelper.getDecrypted(
+		additionalData,
 		nodeCredentials,
 		type,
 		mode,