Export GOVUKFrontendConfigurableComponent as part of the public API

[romaricpascal]

What

After deciding on a final name for the class, rename the GOVUKFrontendComponentConfigurable class created in #5456 and export it as part of the public API.

Important

The PR for this piece of work should only be merged once we've used the feature in the Design System site through a preview branch and we have documentation ready on the Frontend Docs

Why

So people can use it in their components

Who needs to work on this

Developers

Who needs to review this

Developers

Done when

• Name has been agreed for the class
• all.mjs exports the class