Support for setting publish date through WC API

[callumstrubi]

Prerequisites

• I have searched for similar issues in both open and closed tickets and cannot find a duplicate
• The issue still exists against the latest master branch of WooCommerce on Github (this is not the same version as on WordPress.org!)
• I have attempted to find the simplest possible steps to reproduce the issue
• I have included a failing test as a pull request (Optional)

Steps to reproduce the issue

1. Setting a date field within the woocommerce product data does not affect the publish-date of the resulting product.

Expected/actual behavior

Isolating the problem

• This bug happens with only WooCommerce plugin active
• This bug happens with a default WordPress theme active, or Storefront
• I can reproduce this bug consistently using the steps above

[mikejolley]

The API docs here indicate this is a read only field:

https://woocommerce.github.io/woocommerce-rest-api-docs/#product-properties

I've logged a question in the development branch for the API woocommerce/wc-api-dev#104