Update the LLM Agents guide with Gemini2.0 Thinking demo

[yvrjsharma]

Description

Added Guide for Gemini2.0 Flash Thinking.

Closes: #(issue)

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[abidlabs]

LGTM @yvrjsharma left some suggestions but nothing major

[yvrjsharma]

I've addressed all comments. Will go ahead and merge as discussed on Slack @abidlabs.