Propagate sampling decision as attribute (aws-observability#1161)

Author: majanjua-amzn

awsagentprovider/src/main/java/software/amazon/opentelemetry/javaagent/providers/AttributePropagatingSpanProcessor.java

@@ -112,6 +112,7 @@ public void onStart(Context parentContext, ReadWriteSpan span) {
     if (propagationData != null) {
       span.setAttribute(propagationDataKey, propagationData);
     }
+    span.setAttribute(AwsAttributeKeys.AWS_TRACE_FLAG_SAMPLED, span.getSpanContext().isSampled());
   }
 
   private boolean isConsumerKind(ReadableSpan span) {

awsagentprovider/src/main/java/software/amazon/opentelemetry/javaagent/providers/AwsAttributeKeys.java

@@ -106,9 +106,6 @@ private AwsAttributeKeys() {}
   static final AttributeKey<Boolean> AWS_TRACE_FLAG_SAMPLED =
       AttributeKey.booleanKey("aws.trace.flag.sampled");
 
-  static final AttributeKey<String> AWS_XRAY_SAMPLING_RULE =
-      AttributeKey.stringKey("aws.xray.sampling_rule");
-
   // use the same AWS Resource attribute name defined by OTel java auto-instr for aws_sdk_v_1_1
   // TODO: all AWS specific attributes should be defined in semconv package and reused cross all
   // otel packages. Related sim -