Add ETag to `/custom_component` route to control browser caching

[freddyaboulton]

Description

Setting an ETag in the response of /custom_component that's equal to the hash of the requested file. I think this is preferable than setting a max-age because it should minimize the chance of a stale cache. During development, it's possible to build frequently to see if latest changes work outside the development server ( I do that atleast) so the max-age would be hard to set in this case.

Closes: #8168

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[gradio-pr-bot]

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Install Gradio from this PR

pip install https://gradio-builds.s3.amazonaws.com/6fff2d0cc8cabcfb835df9dbc2e71cf2cc4e6ff8/gradio-4.28.3-py3-none-any.whl

Install Gradio Python Client from this PR

pip install "gradio-client @ git+https://github.com/gradio-app/gradio@6fff2d0cc8cabcfb835df9dbc2e71cf2cc4e6ff8#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 ETag to /custom_component route to control browser caching

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[freddyaboulton]

Thanks for the review @pngwn !!