feat: Enable leader aware routing by default (#2538)

BEGIN_COMMIT_OVERRIDE feat: Enable leader aware routing by default. This update contains performance optimisations that will reduce the latency of read/write transactions that originate from a region other than the default leader region. END_COMMIT_OVERRIDE

Author: yifanzyifanz

google-cloud-spanner/src/main/java/com/google/cloud/spanner/SpannerOptions.java

@@ -702,7 +702,7 @@ public static class Builder
  private CloseableExecutorProvider asyncExecutorProvider;
  private String compressorName;
  private String emulatorHost = System.getenv("SPANNER_EMULATOR_HOST");
- private boolean leaderAwareRoutingEnabled = false;
+ private boolean leaderAwareRoutingEnabled = true;
 
  private Builder() {
  // Manually set retry and polling settings that work.

google-cloud-spanner/src/test/java/com/google/cloud/spanner/SpannerOptionsTest.java

@@ -680,8 +680,7 @@ public void testCompressorName() {
 
  @Test
  public void testLeaderAwareRoutingEnablement() {
- assertFalse(
- SpannerOptions.newBuilder().setProjectId("p").build().isLeaderAwareRoutingEnabled());
+ assertTrue(SpannerOptions.newBuilder().setProjectId("p").build().isLeaderAwareRoutingEnabled());
  assertTrue(
  SpannerOptions.newBuilder()
  .setProjectId("p")