ProductAttribute json/api structure and minimum amounts for one-time and recurring donations

donate-neo will have a JSON file that reads product information. That JSON will be generated by CiviCRM. Initially it was supposed to be an API query, but to firewall things in the short-term, CRM admins will have to copy-paste a JSON blob generated by the CiviCRM API Explorer into a Gitlab file, which will then get deployed to prod.

Some proof of concept has already been done, but the JSON needed some changes:

• Structure the product attribute sizes by fit product_id.optionsForDonateNeo
• Add the minimum one-time amount (this is a core field, product_id.min_contribution)
• Add the minimum recurring amount (this will require a custom field, product_id.Swag.Minimum_Recurring_Amount)
• Add the image as a base64 blob product_id.imageForDonateNeo
• Have an easier way to generate the JSON, and in the right format

cc @stephen @mattlav (fyi)