Deprecate setPaymentMethodAndPlaceOrderMutation

[pmclain]

Description (*)

The #723 introduces setPaymentAndPlaceOrder mutation to set the payment method for the cart and place an order via the same mutation.
After internal discussion, we decided to remove setPaymentAndPlaceOrder as GraphQL guarantees that multiple mutations will be executed one by one via one HTTP request https://graphql.org/learn/queries/.

Fixed Issues (if relevant)

1. [Checkout] Remove setPaymentAndPlaceOrder mutation #875

Manual testing scenarios (*)

1. Create empty cart
2. Add product to cart
3. Set shipping address and method (if cart is not virtual)
4. Set billing address

mutation {
  setPaymentMethodOnCart(
    input: {
      cart_id: "{$maskedQuoteId}"
      payment_method: {
        code: "{$methodCode}"
      }
    }
  ) {
    cart {
      selected_payment_method {
        code
      }
    }
  }
  placeOrder(
    input: {
      cart_id: "{$maskedQuoteId}"
    }
  ) {
    order {
      order_id
    }
  }
}

Contribution checklist (*)

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds are green)

[magento-engcom-team]

Hi @lenaorobei, thank you for the review.
ENGCOM-5814 has been created to process this Pull Request

[ghost]

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