Adding image decoding

[rafaelstz]

WHY are these changes introduced?

The decoding property is auto by default, but in order to improve the LCP and CLS scores we can use it as sync to prioritize it.
Introducing these changes, give the dev the possibility to use it in other image elements easier.

WHAT is this pull request doing?

Adding the decoding='sync' to Hero images and adding the decoding capability to the SpreadMedia component.

HOW to test your changes?

Through the Network tab, check the feels like during the loading, the prioritization, and the browser compatibilities.
https://developer.mozilla.org/en-US/docs/Web/API/HTMLImageElement/decoding

Post-merge steps

Checklist

• I've read the Contributing Guidelines
• I've considered possible cross-platform impacts (Mac, Linux, Windows)
• I've added a changeset if this PR contains user-facing or noteworthy changes
• I've added tests to cover my changes
• I've added or updated the documentation

[juanpprieto]

@rafaelstz thanks for this contribution.

Could you please add a chageset by running npm run changeset at the root and selecting

• create-hydrogen (affected package)
• patch release (will be selected when you ignore major and minor releases options)
• add a changeset message 🙏🏼

[rafaelstz]

All set @juanpprieto