feat: Added Agentic Search Cookbook

[JoyceXu02]

Description

Added agent search cookbook to the docs

Checklist

Go over all the following points, and put an x in all the boxes that apply.

• [x] I have read the CONTRIBUTION guide (required)
• [x] I have linked this PR to an issue using the Development section on the right sidebar or by adding Fixes #issue-number in the PR description (required)
• [x] I have checked if any dependencies need to be added or updated in pyproject.toml and uv lock
• [x] I have updated the tests accordingly (required for a bug fix or a new feature)
• [x] I have updated the documentation if needed:
• [x] I have added examples if this is a new feature

Fix #1686