chore: update NpmPackage assets reference

[caalador]

Update the npm assets referencing to match
new functionality.

part of vaadin/flow#22515

[github-actions]

AI Language Review

• In the section under "[#fonts-and-images-from-npm]", the phrase "starting the request as assets/{npm_asset_path}" seems unclear and unnecessary. Consider rephrasing or removing if this is not providing critical information.
• In the example usage of the assets field, the description of the SVG file path needs to ensure consistency with the description. It mentions "assets/fontawesome/icons/snowflake.svg" in the code example, but in the explanation, it refers to "VAADIN/static/assets/fontawesome/icons/snowflake.svg". Confirm the intended asset directory to avoid confusion.