Update GraphQL queries

[orzechdev]

I want to merge this change because current storefront doesn't work with the latest API, what this PR should fix.

Screenshots

Pull Request Checklist

1. All visible strings are translated with proper context.
2. All data-formatting is locale-aware (dates, numbers, and so on).
3. The changes are tested.
4. The code is documented (docstrings, project documentation).
5. Changes are mentioned in the changelog.

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[maarcingebala]

This field requires a staff permission - which means it's meant for the dashboard app. I know it's kind of messed up together - we need to have separate API for storefront and dashboard.

Public pricing should be taken from the pricing field.

[maarcingebala]

The product's price is a range since we can override the price for one of its variants. To get this range we can use:

pricing {
  priceRange {
    start {
      net {
        amount
      }
    }
    stop {
      net {
        amount
      }
    }
  }
}

Example response:

"pricing": {
  "priceRange": {
    "start": {
      "net": {
        "amount": 1.8
      }
    },
    "stop": {
      "net": {
        "amount": 4.2
      }
    }
  }
}

In this case, in the product page, we should render the price as "From $1.8". If the amounts were equal then we could render the precise value. That's the logic we used to have in the old storefront in the good old Django-templates times ;)

[orzechdev]

I fixed it with rendering range e.g. "1,80 USD - 4,20 USD" if values are not equal, similarly as it is rendered when variants exist.

[orzechdev]

But I used gross value... Does it matter?

[maarcingebala]

It's fine to use gross prices for now. Eventually, it should depend on this setting:

{
  shop {
    displayGrossPrices
  }
}

But it can be done in a separate PR (we have an issue for that)

[domantasjurkus]

A new stable release with this fix has note been drafted - following the README of saleor-storefront, running the 0.7.0 version throws the same 400 bad requests. Could you draft a new release?