[ML] Feature flag default configs (elastic#114660)

Author: davidkyle

x-pack/plugin/inference/src/main/java/org/elasticsearch/xpack/inference/InferencePlugin.java

@@ -217,8 +217,10 @@ public Collection<?> createComponents(PluginServices services) {
         // reference correctly
         var registry = new InferenceServiceRegistry(inferenceServices, factoryContext);
         registry.init(services.client());
-        for (var service : registry.getServices().values()) {
-            service.defaultConfigs().forEach(modelRegistry::addDefaultConfiguration);
+        if (DefaultElserFeatureFlag.isEnabled()) {
+            for (var service : registry.getServices().values()) {
+                service.defaultConfigs().forEach(modelRegistry::addDefaultConfiguration);
+            }
         }
         inferenceServiceRegistry.set(registry);
 

x-pack/plugin/src/yamlRestTest/resources/rest-api-spec/test/inference/inference_crud.yml

@@ -41,6 +41,10 @@
 
 ---
 "Test get all":
+  - requires:
+      cluster_features: "semantic_text.default_elser_2"
+      reason: semantic_text default ELSER 2 inference ID introduced in 8.16.0
+      
   - do:
       inference.get:
         inference_id: "*"