Fix Request Bodies in API Documentation

[kennyadsl]

Description

As raised in #4058 and #3983, we are documenting all our POST/PUT/PATCH API endpoints wrongly.

We need to wrap the JSON of the request body with the object name that we are trying to create/edit. This is a example of the correct format, that we will have after this PR is merged:

 {
  "product": {
    "name": "Product Name",
    "other": "fields"
   }
}

But we are currently documenting all the endpoints to be used as:

{
  "name": "Product Name",
  "other": "fields"
}

Enpoints Fixed:

• product
• variant
• payment
• address
• line-item
• checkout
• order
• coupon-code
• shipment
• zone
• product-property
• stock-location
• taxon
• taxonomy
• property
• image
• user
• return-authorization
• customer-return
• option-value
• stock-item

How to test this PR's result:

Create a new project in Stoplight Studio, copy/paste the resulting oas.yml file, which should be available here and watch the preview for the result.

Checklist:

• I have followed Pull Request guidelines
• I have added a detailed description into each commit message
• I have updated Guides and README accordingly to this change (if needed)
• I have added tests to cover this change (if needed)
• I have attached screenshots to this PR for visual changes (if needed)

[gmacdougall]

I trust that you did this right.