feat: Optimise langchain calls in batching mode (#15243)

packages/@n8n/nodes-langchain/nodes/chains/ChainRetrievalQA/constants.ts

@@ -0,0 +1,20 @@
+import type { INodeProperties } from 'n8n-workflow';
+
+export const SYSTEM_PROMPT_TEMPLATE = `You are an assistant for question-answering tasks. Use the following pieces of retrieved context to answer the question.
+If you don't know the answer, just say that you don't know, don't try to make up an answer.
+----------------
+Context: {context}`;
+
+// Due to the refactoring in version 1.5, the variable name {question} needed to be changed to {input} in the prompt template.
+export const LEGACY_INPUT_TEMPLATE_KEY = 'question';
+export const INPUT_TEMPLATE_KEY = 'input';
+
+export const systemPromptOption: INodeProperties = {
+	displayName: 'System Prompt Template',
+	name: 'systemPromptTemplate',
+	type: 'string',
+	default: SYSTEM_PROMPT_TEMPLATE,
+	typeOptions: {
+		rows: 6,
+	},
+};