chore: Deprecate Zep nodes (#18061)

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

packages/@n8n/nodes-langchain/credentials/ZepApi.credentials.ts

@@ -13,6 +13,12 @@ export class ZepApi implements ICredentialType {
 	documentationUrl = 'zep';
 
 	properties: INodeProperties[] = [
+		{
+			displayName: 'This Zep integration is deprecated and will be removed in a future version.',
+			name: 'deprecationNotice',
+			type: 'notice',
+			default: '',
+		},
 		{
 			displayName: 'API Key',
 			name: 'apiKey',