workflow: add html modality

[hannahblair]

Description

adds an html modality to preview html outputs

[gradio-pr-bot]

🪼 branch checks and previews

•	Name	Status	URL
	Spaces	ready!	Spaces preview
	Storybook	ready!	Storybook preview
🦄	Changes	detected!	Details

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Install Gradio from this PR

pip install https://huggingface.co/buckets/gradio/pypi-previews/resolve/f8b8c04be96d26afcfafb9bccb225f32e86a4fa2/gradio-6.20.0-py3-none-any.whl

Install Gradio Python Client from this PR

pip install "gradio-client @ git+https://github.com/gradio-app/gradio@f8b8c04be96d26afcfafb9bccb225f32e86a4fa2#subdirectory=client/python"

Import Gradio JS Client from this PR via CDN

import { Client } from "https://huggingface.co/buckets/gradio/npm-previews/resolve/f8b8c04be96d26afcfafb9bccb225f32e86a4fa2/browser.js";

[gradio-pr-bot]

🦄 change detected

This Pull Request includes changes to the following packages.

Package	Version
@gradio/workflowcanvas	minor
gradio	minor

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• workflow: add html modality

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Something isn't right?

• Maintainers can change the version label to modify the version bump.
• If the bot has failed to detect any changes, or if this pull request needs to update multiple packages to different versions or requires a more comprehensive changelog entry, maintainers can update the changelog file directly.

[abidlabs]

Nice LGTM, will merge this in.