feat: enable trailer optimization by default (#2421)

This should save ~300-500u for readRow calls

Change-Id: Idcf531e2db0e9c751c87f3522c8a2ad4733923d6

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Fixes #<issue_number_goes_here> ☕️

If you write sample code, please follow the [samples format](
https://togithub.com/GoogleCloudPlatform/java-docs-samples/blob/main/SAMPLE_FORMAT.md).

google-cloud-bigtable/src/main/java/com/google/cloud/bigtable/data/v2/stub/EnhancedBigtableStubSettings.java

@@ -112,7 +112,7 @@ public class EnhancedBigtableStubSettings extends StubSettings<EnhancedBigtableS
   private static final boolean SKIP_TRAILERS =
       Optional.ofNullable(System.getenv("CBT_SKIP_HEADERS"))
           .map(Boolean::parseBoolean)
-          .orElse(DIRECT_PATH_ENABLED);
+          .orElse(true);
 
   private static final Set<Code> IDEMPOTENT_RETRY_CODES =
       ImmutableSet.of(Code.DEADLINE_EXCEEDED, Code.UNAVAILABLE);