Proposal: Add standalone Function Calling sample using ChatClient Fluent API

[hasiniran]

Description

I would like to contribute a new sample module to models/chat that demonstrates AI Function Calling (Tools) using the modern ChatClient Fluent API.

While there are functional tests for this feature, a dedicated, beginner-friendly sample would help developers understand how to bridge existing Java services with LLMs.

Proposed Implementation

The sample will include:

1. Tool Definition: A simple @bean function (e.g., a Weather or Stock price mock) using the 'Function' interface.
2. ChatClient Integration: Demonstrating how to register the function using .functions("functionName") within the fluent API.
3. Observability: Integration of SimpleLoggerAdvisor to show the underlying "Tool Call" interaction in the console logs—essential for debugging agentic behavior.
4. Local-First: Configuration optimized for Ollama (llama3.2) to ensure users can run it without requiring external API keys.

Why this is valuable

Function calling is a core "Agentic" feature of Spring AI. This sample provides a clear "Hello World" for connecting LLMs to external Java logic, which is a primary use case for enterprise developers.

I would love to submit a PR if the maintainers find this valuable!