feat: Add AI tool building capabilities (#7336)

Github issue / Community forum post (link here to close automatically):
https://community.n8n.io/t/langchain-memory-chat/23733

---------

Signed-off-by: Oleg Ivaniv <me@olegivaniv.com>
Co-authored-by: Oleg Ivaniv <me@olegivaniv.com>
Co-authored-by: Val <68596159+valya@users.noreply.github.com>
Co-authored-by: Alex Grozav <alex@grozav.com>
Co-authored-by: कारतोफ्फेलस्क्रिप्ट™ <aditya@netroy.in>
Co-authored-by: Deborah <deborah@starfallprojects.co.uk>
Co-authored-by: Jesper Bylund <mail@jesperbylund.com>
Co-authored-by: Jon <jonathan.bennetts@gmail.com>
Co-authored-by: Michael Kret <88898367+michael-radency@users.noreply.github.com>
Co-authored-by: Giulio Andreini <andreini@netseven.it>
Co-authored-by: Mason Geloso <Mason.geloso@gmail.com>
Co-authored-by: Mason Geloso <hone@Masons-Mac-mini.local>
Co-authored-by: Mutasem Aldmour <mutasem@n8n.io>

packages/@n8n/nodes-langchain/nodes/agents/OpenAiAssistant/utils.ts

@@ -0,0 +1,47 @@
+import { zodToJsonSchema } from 'zod-to-json-schema';
+import type { OpenAI as OpenAIClient } from 'openai';
+import type { StructuredTool } from 'langchain/tools';
+
+// Copied from langchain(`langchain/src/tools/convert_to_openai.ts`)
+// since these functions are not exported
+
+/**
+ * Formats a `StructuredTool` instance into a format that is compatible
+ * with OpenAI's ChatCompletionFunctions. It uses the `zodToJsonSchema`
+ * function to convert the schema of the `StructuredTool` into a JSON
+ * schema, which is then used as the parameters for the OpenAI function.
+ */
+export function formatToOpenAIFunction(
+	tool: StructuredTool,
+): OpenAIClient.Chat.ChatCompletionCreateParams.Function {
+	return {
+		name: tool.name,
+		description: tool.description,
+		parameters: zodToJsonSchema(tool.schema),
+	};
+}
+
+export function formatToOpenAITool(tool: StructuredTool): OpenAIClient.Chat.ChatCompletionTool {
+	const schema = zodToJsonSchema(tool.schema);
+	return {
+		type: 'function',
+		function: {
+			name: tool.name,
+			description: tool.description,
+			parameters: schema,
+		},
+	};
+}
+
+export function formatToOpenAIAssistantTool(
+	tool: StructuredTool,
+): OpenAIClient.Beta.AssistantCreateParams.AssistantToolsFunction {
+	return {
+		type: 'function',
+		function: {
+			name: tool.name,
+			description: tool.description,
+			parameters: zodToJsonSchema(tool.schema),
+		},
+	};
+}