[productcatalog] - allow products to be extended

[puckpuck]

Changes

Now that we have the mountedConfigMaps feature in Helm charts, allowing people to add text-based configuration or data files to any components, we can setup the productcatalog service to have the product list extended.

1. It removes the image path prefix from the catalog itself. This is a frontend implementation detail, so that detail should live within the frontend.
2. Moves the products.json file into a folder, and changes code to load all .json files from that folder.

With this change, using the Helm chart you can add new products like this:

components:
  productCatalogService:
    mountedConfigMaps:
      - name: extraProducts
        mountPath: /usr/src/app/products/extra.json
        subPath: extra.json
        data:
          extra.json: |
            {"products":[ ... ]}

This could also be done with a volume mount in docker compose.

Merge Requirements

For new features contributions please make sure you have completed the following
essential items:

• CHANGELOG.md updated to document new feature additions
• Appropriate documentation updates in the docs
• Appropriate Helm chart updates in the helm-charts

Maintainers will not merge until the above have been completed. If you're unsure
which docs need to be changed ping the
@open-telemetry/demo-approvers.

[julianocosta89]

🚀