Added forceToken support for pricing endpoints

[MiChAeLoKGB]

Fixes #28

For PriceProtectionException to work, API must return PRICE_PROTECTION_ERROR instead of generic VALIDATION_ERROR when price protection mechanism is tripped.

[DRN88]

Why is this still not merged? This exception happens all the time.

vendor/mallgroup/mpapi-client/src/Article/ArticleClient.php

    public function updateProduct(ProductRequest $product): void
    {
        $this->sendJson('PUT', sprintf(self::PRODUCT_DETAIL, $product->getId()), $product->getArrayForApi());
    }

    public function updateProductWithForceToken(ProductRequest $product, string $forceToken): void
    {
        $appendUrlWithForceToken = '?force_token=' . $forceToken;
        $this->sendJson('PUT', sprintf(self::PRODUCT_DETAIL, $product->getId()) . $appendUrlWithForceToken, $product->getArrayForApi());
    }

    public function deleteProduct(string $productId): void
    {
        $this->sendJson('DELETE', sprintf(self::PRODUCT_DETAIL, $productId));
    }

In a try-catch, get the force token, and use updateProductWithForceToken to update the product.