Update ShipDate handling in GetRatesRequest

Modified the ShipDate property to use the shipping date
from shipment.Options instead of the current UTC time.
This change improves accuracy in shipping date management
based on user input.

src/EasyKeys.Shipping.Amazon.Rates/AmazonShippingRateProvider.cs

@@ -34,7 +34,7 @@ public async Task<Shipment> GetRatesAsync(Shipment shipment,RateContactInfo rate
         {
             var rateRequest = new GetRatesRequest()
             {
-                ShipDate = DateTime.Now.ToUniversalTime().ToString("yyyy-MM-dd'T'HH:mm:ss'Z'"),
+                ShipDate = shipment.Options.ShippingDate.ToString("yyyy-MM-dd'T'HH:mm:ss'Z'"),
                 ShipTo = new Abstractions.OpenApis.V2.Shipping.Address()
                 {
                     AddressLine1 = shipment.DestinationAddress.StreetLine,