feat: create node for local assets and webp asset support

[notrab]

• fix: use createNodeField for remote node

• chore: update demo to use downloadLocalImages

• fix: set File field link

[gatsby-cloud[bot]]

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Accessibility	:green_heart: 93
Best Practices	:green_heart: 100
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[github-actions[bot]]

:tada: This PR is included in version 2.8.0 :tada:

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