Add guide on Client state and and fix default values of components

[abidlabs]

Fixes: #4175

Also sets the default values of several components to None instead of an empty string. This makes no difference in the Gradio app itself, but it makes a difference when connecting from the client as any non-None value means that the parameter is not required, which can be confusing if a user did not intentionally specify a non-None value.

[gradio-pr-bot]

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Install Gradio from this PR

pip install https://gradio-builds.s3.amazonaws.com/6f3d014905a0e6ebfa595980d809ffec57be45f0/gradio-4.23.0-py3-none-any.whl

Install Gradio Python Client from this PR

pip install "gradio-client @ git+https://github.com/gradio-app/gradio@6f3d014905a0e6ebfa595980d809ffec57be45f0#subdirectory=client/python"

[gradio-pr-bot]

🦄 change detected

This Pull Request includes changes to the following packages.

Package	Version
gradio	patch

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With the following changelog entry.

Add guide on Client state and and fix default values of components

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[aliabd]

LGTM with one comment