Make Advice proper immutable class (#5532)

Signed-off-by: Bogdan Drutu <bogdandrutu@gmail.com>

sdk/metrics/src/main/java/io/opentelemetry/sdk/metrics/internal/descriptor/Advice.java

@@ -6,6 +6,8 @@
 package io.opentelemetry.sdk.metrics.internal.descriptor;
 
 import com.google.auto.value.AutoValue;
+import java.util.ArrayList;
+import java.util.Collections;
 import java.util.List;
 import javax.annotation.Nullable;
 import javax.annotation.concurrent.Immutable;
@@ -20,7 +22,17 @@ public static Advice empty() {
     return EMPTY_ADVICE;
   }
 
+  /**
+   * Creates a new {@link Advice} with the given explicit bucket histogram boundaries.
+   *
+   * @param explicitBucketBoundaries the explicit bucket histogram boundaries.
+   * @return a new {@link Advice} with the given bucket boundaries.
+   */
   public static Advice create(@Nullable List<Double> explicitBucketBoundaries) {
+    if (explicitBucketBoundaries != null) {
+      explicitBucketBoundaries =
+          Collections.unmodifiableList(new ArrayList<>(explicitBucketBoundaries));
+    }
     return new AutoValue_Advice(explicitBucketBoundaries);
   }