feat: add search tool to FileToolkit

[hesamsheikh]

Description

part of #3265. This PR adds a search tool that can be used to find patterns in specific files. The same functionality could be achieved in the TerminalToolkit through custom commands such as grep, but that would be hard to control and too broad.

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✨ Finishing touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
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• Commit unit tests in branch add-search-files-to-file-toolkit

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[Wendong-Fan]

thanks @hesamsheikh , overall LGTM, will add another PR for minor enhance