Update version to 5.4.0 and refactor rate request handling

Updated `GitVersion.yml` to set the next version to `5.4.0` and modified the `feature` branch configuration to include a `preview` tag and `patch` increment.

Removed the handling of `RateRequestTypes` in `FedExShipmentProvider.cs`, simplifying the code while retaining the existing logic for processing `DropoffType`.

Author: Brandon Moffett

GitVersion.yml

@@ -1,5 +1,5 @@
 mode: Mainline
-next-version: 5.3.0
+next-version: 5.4.0
 branches:
   feature:
     tag: preview

src/EasyKeys.Shipping.FedEx.Shipment/WebServices/Impl/FedExShipmentProvider.cs

@@ -300,14 +300,6 @@ private void SetShipmentDetails(
                 Units = WeightUnits.LB
             },
 
-            RateRequestTypes = details.RateRequestType.ToLower() switch
-            {
-                "none" => new RateRequestType[1] { RateRequestType.NONE },
-                "list" => new RateRequestType[1] { RateRequestType.LIST },
-                "preferred" => new RateRequestType[1] { RateRequestType.PREFERRED },
-                _ => throw new NotImplementedException(),
-            },
-
             DropoffType = shipment.Options.DropOffType.ToLower() switch
             {
                 "regularpickup" => DropoffType.REGULAR_PICKUP,