Add the full store demo recipe to the Composer project template

Converting this into a meta ticket so we can create child tickets pertaining to each task.

I will be documenting issues that I've encountered while working on this.

- Default Content importer in core behavior when handling files is different than the one from default_content module. The lookup for the source file happens based on the destination filename, and not the source filename.

- Default Content importer in core can't handle product/product_variation import. This is partially due to circular dependency between Product and Product Variation - Product depends on Product Variation via variations base field set as required, and Product Variation depends on Product via product_id which is presented as a dependency in content yml file - example. The root cause is the Importer in core performing content validation prior save which wasn't a case for Importer in default_content module.

- And one more 🐛 Warnings logged for missing field block plugins when enabling layout builder on an entity view display for the first time Active - don't believe it is a blocker, just gives buggy feedback during recipe application.

One more bug - the front page doesn't look great after the default content import. This is likely due to entity id references being used vs uuids (ie. media_id vs media_uuid). Otherwise, POC looks ok.

However, before closing this meta, I think at least one more thing must be done. Recipes can be installed on any existing Drupal site, especially on existing commerce sites built with commerce_kickstart and already customized. I believe commerce_kickstart_demo should take precautions and not apply if it is to modify the existing site (site where certain config entries already exist). For example - if product_collections vocabulary already exists the recipe should not attempt to rewrite it but it should fail instead. This should be possible with setting the config.strict: true

Yeah, let's not close this out until we're done with the 1:1 replacement of Commerce Demo with Commerce Kickstart Demo. 😄

Retitling for accuracy, making a separate task for project template updating.

All issues were addressed. I will be tagging the stable release soon.