feat(simple-pricing): Compute displayPrice as resolver as needed

[focusaurus]

Impact: minor
Type: feature

Issue

With the existing simple-pricing core plugin flow, catalogProduct.product.pricing.displayPrice is computed at publication time (ahead of time) and stored in mongodb. For the in-development Catalog Publisher component, doing the computation of displayPrice at publish time would require the full set of currency formatting I18N data and logic to be available in kafka and kafka streams.

Solution

Allow displayPrice to be computed at query time via a graphql resolver if necessary. This implementation works seamlessly with both the core simple-pricing plugin as before, but computes displayPrice as needed if the catalog plugin is disabled in favor of the catalog publisher service in a particular deployment. No configuration is necessary and data could in theory even be mixed between catalog plugin and catalog publisher.

Breaking changes

This should be fully compatible with existing clients and installations.

Testing

A unit test has been added. Manual testing is still planned/underway so I'll convert to ready for review when that is completed.

At the moment catalog publisher output data is arriving in the Catalog2 collection in mongodb which is not used at all by reaction core or plugins. To test this we'd need to retarget or rename that so it's the real Catalog collection. Undoubtedly the first time we do that some bugs will surface which we'll have to fix. Once those are fixed though, we should now be able to test this PR. If you query graphql with a query similar to below, and the displayPrice attribute looks correct, this change is working properly.

query {
  catalogItemProduct(shopId: "cmVhY3Rpb24vc2hvcDpKOEJocTN1VHRkZ3daeDNyeg==", slugOrId: "timberlands") {
    product {
      pricing {
        currency {
          rate
        }
        compareAtPrice {
          amount
        }
        displayPrice
        
      }
    }
  }
}# Write your query or mutation here

[rosshadden]

I approve the idea and the implementation. I haven't tested manually or run the newly-added test, but when this moves out of draft mode I'll spin it up and do so.

[focusaurus]

I was able to checkout with this. Seems to be working OK.