Expose isSampled on TraceContext; fixes gh-1799

spring-cloud-sleuth-api/src/main/java/org/springframework/cloud/sleuth/TraceContext.java

@@ -45,4 +45,9 @@ public interface TraceContext {
 	 */
 	String spanId();
 
+	/**
+	 * @return {@code true} when sampled
+	 */
+	boolean isSampled();
+
 }

spring-cloud-sleuth-autoconfigure/src/test/java/org/springframework/cloud/sleuth/autoconfig/NoOpTraceContext.java

@@ -41,4 +41,9 @@ class NoOpTraceContext implements TraceContext {
 		return "";
 	}
 
+	@Override
+	public boolean isSampled() {
+		return false;
+	}
+
 }

spring-cloud-sleuth-brave/src/main/java/org/springframework/cloud/sleuth/brave/bridge/BraveTraceContext.java

@@ -51,6 +51,11 @@ class BraveTraceContext implements TraceContext {
 		return this.traceContext.spanIdString();
 	}
 
+	@Override
+	public boolean isSampled() {
+		return this.traceContext.sampled();
+	}
+
 	@Override
 	public String toString() {
 		return this.traceContext != null ? this.traceContext.toString() : "null";

spring-cloud-sleuth-otel/src/main/java/org/springframework/cloud/sleuth/otel/bridge/OtelTraceContext.java

@@ -99,6 +99,11 @@ class OtelTraceContext implements TraceContext {
 		return this.delegate.getSpanIdAsHexString();
 	}
 
+	@Override
+	public boolean isSampled() {
+		return this.delegate.isSampled();
+	}
+
 	@Override
 	public String toString() {
 		return this.delegate != null ? this.delegate.toString() : "null";