Log warning when ServiceUrl and RegionEndpoint are set at the same time (#3732)

* Log warning when ServiceUrl and RegionEndpoint are set at the same time

Author: peterrsongg

generator/.DevConfigs/62a70097-c6d6-4566-907b-20b48b2764d4.json

@@ -0,0 +1,9 @@
+{
+    "core": {
+      "changeLogMessages": [
+        "Log a warning when ServiceUrl and Region Endpoint are set at the same time. The SDK will log whichever of the two is used."
+      ],
+      "type": "patch",
+      "updateMinimum": true
+    }
+  }

sdk/src/Core/Amazon.Runtime/ClientConfig.cs

@@ -271,6 +271,9 @@ public RegionEndpoint RegionEndpoint
             }
             set
             {
+                if (!string.IsNullOrEmpty(this.serviceURL))
+                    Logger.GetLogger(GetType()).InfoFormat($"RegionEndpoint and ServiceURL are mutually exclusive. Since " +
+                        $"RegionEndpoint was set last, RegionEndpoint: {value} will be used to make the request and ServiceUrl: {this.serviceURL} has been set to null.");
                 this.defaultConfigurationBackingField = null;
                 this.serviceURL = null;
                 this.regionEndpoint = value;
@@ -373,6 +376,9 @@ public string ServiceURL
             }
             set
             {
+                if (regionEndpoint != null)
+                    Logger.GetLogger(GetType()).InfoFormat($"RegionEndpoint and ServiceURL are mutually exclusive. Since " +
+                        $"ServiceUrl was set last, ServiceUrl: {value} will be used to make the request and RegionEndpoint: {this.regionEndpoint} has been set to null.");
                 this.regionEndpoint = null;
                 this.probeForRegionEndpoint = false;