Mark the features_supported feature as assumed (#118849) (#119496)

Only do one here so we can verify the mechanisms

Author: thecoop

server/src/main/java/org/elasticsearch/features/FeatureService.java

@@ -32,7 +32,7 @@ public class FeatureService {
     /**
      * A feature indicating that node features are supported.
      */
-    public static final NodeFeature FEATURES_SUPPORTED = new NodeFeature("features_supported");
+    public static final NodeFeature FEATURES_SUPPORTED = new NodeFeature("features_supported", true);
     public static final NodeFeature TEST_FEATURES_ENABLED = new NodeFeature("test_features_enabled");
 
     private static final Logger logger = LogManager.getLogger(FeatureService.class);

server/src/main/java/org/elasticsearch/features/NodeFeature.java

@@ -17,7 +17,7 @@
  * @param id        The feature id. Must be unique in the node.
  * @param assumedAfterNextCompatibilityBoundary
  *              {@code true} if this feature is removed at the next compatibility boundary (ie next major version),
- *              and so should be assumed to be true for all nodes after that boundary.
+ *              and so should be assumed to be met by all nodes after that boundary, even if they don't publish it.
  */
 public record NodeFeature(String id, boolean assumedAfterNextCompatibilityBoundary) {