2024-04: clarify Image.source description

[ryan-ludwig]

Background

Part of https://github.com/Shopify/checkout-web/issues/31776. Updates the docs for the 2024-04 stable release.

There is another PR in this repo to update the unstable channel docs.

A follow up to https://github.com/Shopify/checkout-web/pull/31805

[github-actions]

We detected some changes in packages/*/package.json or packages/*/src, and there are no updates in the .changeset directory. If the changes are user-facing and should cause a version bump, run yarn changeset to track your changes and include them in the next release CHANGELOG. If you are making simple updates to repo configuration, examples, or documentation, you do not need to add a changeset.

[oliverigor]

I would wait for James as he will help adding changelogs to this :D

[jamesvidler]

These updates have already been merged in 2024-04 earlier today.