[BugFix] add fastchat/serve/example_images to wheel

[kota-iizuka]

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Why are these changes needed?

An error occurs when starting gradio_web_server_multi because the wheel package does not contain images under fastchat/serve/example_images/. Modify pyproject.toml to include this directory in the wheel package.

Related issue number (if applicable)

Closes #3111

Checks

• [x] I've run format.sh to lint the changes in this PR.
• [x] I've included any doc changes needed.
• [x] I've made sure the relevant tests are passing (if applicable).