feat: client built in metrics

Author: surbhigarg92

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

@@ -725,7 +725,6 @@ private static class SpannerEnvironmentImpl implements SpannerEnvironment {
         "SPANNER_OPTIMIZER_STATISTICS_PACKAGE";
     private static final String SPANNER_ENABLE_EXTENDED_TRACING = "SPANNER_ENABLE_EXTENDED_TRACING";
     private static final String SPANNER_ENABLE_API_TRACING = "SPANNER_ENABLE_API_TRACING";
-    private static final String SPANNER_ENABLE_BUILTIN_METRICS = "SPANNER_ENABLE_BUILTIN_METRICS";
     private static final String SPANNER_ENABLE_END_TO_END_TRACING =
         "SPANNER_ENABLE_END_TO_END_TRACING";
 
@@ -754,13 +753,6 @@ public boolean isEnableApiTracing() {
       return Boolean.parseBoolean(System.getenv(SPANNER_ENABLE_API_TRACING));
     }
 
-    @Override
-    public boolean isEnableBuiltInMetrics() {
-      // The environment variable SPANNER_ENABLE_BUILTIN_METRICS is used for testing and will be
-      // removed in the future.
-      return Boolean.parseBoolean(System.getenv(SPANNER_ENABLE_BUILTIN_METRICS));
-    }
-
     @Override
     public boolean isEnableEndToEndTracing() {
       return Boolean.parseBoolean(System.getenv(SPANNER_ENABLE_END_TO_END_TRACING));
@@ -828,7 +820,7 @@ public static class Builder
     private OpenTelemetry openTelemetry;
     private boolean enableApiTracing = SpannerOptions.environment.isEnableApiTracing();
     private boolean enableExtendedTracing = SpannerOptions.environment.isEnableExtendedTracing();
-    private boolean enableBuiltInMetrics = SpannerOptions.environment.isEnableBuiltInMetrics();
+    private boolean enableBuiltInMetrics = true;
     private boolean enableEndToEndTracing = SpannerOptions.environment.isEnableEndToEndTracing();
 
     private static String createCustomClientLibToken(String token) {
@@ -1410,8 +1402,9 @@ public Builder setEnableApiTracing(boolean enableApiTracing) {
       return this;
     }
 
-    /** Enabling this will enable built in metrics for each individual RPC execution. */
-    Builder setEnableBuiltInMetrics(boolean enableBuiltInMetrics) {
+    /** Sets whether to enable or disable built in metrics for Data client Operations.
+     * Built in metrics are enabled as default. */
+    public Builder setEnableBuiltInMetrics(boolean enableBuiltInMetrics) {
       this.enableBuiltInMetrics = enableBuiltInMetrics;
       return this;
     }