Update proxy request headers to include startEPK and endEPK

Author: aavasthy

Microsoft.Azure.Cosmos/src/ThinClientStoreClient.cs

@@ -90,7 +90,17 @@ private async ValueTask<HttpRequestMessage> PrepareRequestForProxyAsync(
 
             BufferProviderWrapper bufferProviderWrapper = this.bufferProviderWrapperPool.Get();
             try
-            {
+            {
+                PartitionKeyRange partitionKeyRange = request.RequestContext.ResolvedPartitionKeyRange;
+
+                requestMessage.Headers.TryAddWithoutValidation(
+                    ThinClientConstants.ProxyStartEpk,
+                    partitionKeyRange?.MinInclusive);
+
+                requestMessage.Headers.TryAddWithoutValidation(
+                    ThinClientConstants.ProxyEndEpk,
+                    partitionKeyRange?.MaxExclusive);
+
                 requestMessage.Headers.TryAddWithoutValidation(
                     ThinClientConstants.ProxyOperationType,
                     request.OperationType.ToOperationTypeString());