Query: Fixes logic to determine whether to use distributed query by a…

…dding a check for gateway connection mode (#5024)

## Description

This changes the logic for determining whether to use the distributed
query dedicated gateway.

With this PR, we check both the
**AZURE_COSMOS_DISTRIBUTED_QUERY_GATEWAY_ENABLED** environment variable
**and** the connection mode to determine whether to use the distributed
query dedicated gateway. If the environment variable is set to **True**
**and** the connection mode is **gateway**, then we **will** use the
dedicated gateway. If the connection mode is **direct**, we should not
use the distributed query dedicated gateway.


## Type of change

Please delete options that are not relevant.

- [X] Bug fix (non-breaking change which fixes an issue)
- [] New feature (non-breaking change which adds functionality)
- [] Breaking change (fix or feature that would cause existing
functionality to not work as expected)
- [] This change requires a documentation update

---------

Co-authored-by: neildsh <[email protected]>

Microsoft.Azure.Cosmos/src/Query/v3Query/QueryIterator.cs

@@ -150,7 +150,7 @@ public static QueryIterator Create(
                 returnResultsInDeterministicOrder: queryRequestOptions.ReturnResultsInDeterministicOrder,
                 enableOptimisticDirectExecution: queryRequestOptions.EnableOptimisticDirectExecution,
                 isNonStreamingOrderByQueryFeatureDisabled: queryRequestOptions.IsNonStreamingOrderByQueryFeatureDisabled,
-                enableDistributedQueryGatewayMode: queryRequestOptions.EnableDistributedQueryGatewayMode,
+                enableDistributedQueryGatewayMode: queryRequestOptions.EnableDistributedQueryGatewayMode && (clientContext.ClientOptions.ConnectionMode == ConnectionMode.Gateway),
                 testInjections: queryRequestOptions.TestSettings);
 
             return new QueryIterator(

Microsoft.Azure.Cosmos/tests/Microsoft.Azure.Cosmos.EmulatorTests/Query/DistributedQueryClientTests.cs

@@ -162,6 +162,33 @@ await this.CreateIngestQueryDeleteAsync(
                 ImplementationAsync);
         }
 
+        [TestMethod]
+        public async Task DirectModeTestsAsync()
+        {
+            using EnvironmentVariableOverride enableDistributedQueryOverride = new EnvironmentVariableOverride(
+                ConfigurationManager.DistributedQueryGatewayModeEnabled,
+                bool.TrueString);
+
+            static Task ImplementationAsync(Container container, IReadOnlyList<CosmosObject> _)
+            {
+                TestCase[] testCases = new[]
+                {
+                    MakeTest(
+                        "SELECT VALUE COUNT(1) FROM c",
+                        PageSizes,
+                        Expectations.OneValueWithDocumentCountIsPresent),
+                };
+
+                return RunStreamIteratorTestsAsync(container, testCases);
+            }
+
+            await this.CreateIngestQueryDeleteAsync(
+                ConnectionModes.Direct,
+                CollectionTypes.MultiPartition,
+                CreateDocuments(DocumentCount),
+                ImplementationAsync);
+        }
+
         private static async Task RunPartitionedParityTestsAsync(Container container, IEnumerable<string> testCases)
         {
             IReadOnlyList<FeedRange> feedRanges = await container.GetFeedRangesAsync();
@@ -393,6 +420,11 @@ public static bool AllDocumentsGreaterThan200ArePresent(List<int> actual)
                     .ToHashSet()
                     .SetEquals(actual);
             }
+
+            public static bool OneValueWithDocumentCountIsPresent(List<int> actual)
+            {
+                return (actual.Count == 1) && (actual[0] == DocumentCount);
+            }
         }
 
         private sealed class EnvironmentVariableOverride : IDisposable