Editor Web Component - asset_identifier doesn't load images

[conorriches]

Issue

• On the output-only-wc branch, you could specify an assets identifier - this would load just the assets from the given identifier
• This allows only assets to be loaded, for when we provide code
• This means we don't need to load in code, then immediately overwrite it.

This branch wasn't merged into main intentionally - so the mechanism of asset loading was copied into main separately. Something has stopped working, and assets don't load.

Outcome

Be able to load assets via the asset_identifier prop

[sra405]

knocking this down the road a little given we've got a working solution for BTT beta