docs: Add strict_json_schema and is_enabled to FunctionTool docs

[MuhammadHamidRaza]

This pull request improves the FunctionTool documentation by including two important parameters that were previously missing.

I've noticed that the FunctionTool class in the source code includes strict_json_schema and is_enabled parameters, but these were not listed in the "Custom function tools" section of the documentation.

This update adds these parameters to the documentation, providing a more complete and accurate reference for developers. This change will make it easier for users to understand the full capabilities of the FunctionTool and enhance the overall quality of the SDK's documentation.

[seratch]

Thanks for sending this. However, this reference document page, which is linked from the page, clearly explain what these properties that are not used in the code snippet in the page. Thus, I don't see the necessity to have this change for now.