[ML] Make _inference APIs available in serverless (#105190)

Allow the `_inference` APIs to be called from outside the
Elasticsearch cluster in serverless.

The client annotations still need updating so that the clients
know the APIs exist. But that cannot happen until the APIs
themselves are visible, so this first step makes that happen.

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

@@ -10,6 +10,8 @@ package org.elasticsearch.xpack.inference.rest;
 import org.elasticsearch.client.internal.node.NodeClient;
 import org.elasticsearch.rest.BaseRestHandler;
 import org.elasticsearch.rest.RestRequest;
+import org.elasticsearch.rest.Scope;
+import org.elasticsearch.rest.ServerlessScope;
 import org.elasticsearch.rest.action.RestToXContentListener;
 import org.elasticsearch.xpack.core.inference.action.DeleteInferenceModelAction;
 
@@ -17,6 +19,7 @@ import java.util.List;
 
 import static org.elasticsearch.rest.RestRequest.Method.DELETE;
 
+@ServerlessScope(Scope.PUBLIC)
 public class RestDeleteInferenceModelAction extends BaseRestHandler {
     @Override
     public String getName() {

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

@@ -11,6 +11,8 @@ import org.elasticsearch.client.internal.node.NodeClient;
 import org.elasticsearch.inference.TaskType;
 import org.elasticsearch.rest.BaseRestHandler;
 import org.elasticsearch.rest.RestRequest;
+import org.elasticsearch.rest.Scope;
+import org.elasticsearch.rest.ServerlessScope;
 import org.elasticsearch.rest.action.RestToXContentListener;
 import org.elasticsearch.xpack.core.inference.action.GetInferenceModelAction;
 
@@ -18,6 +20,7 @@ import java.util.List;
 
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 
+@ServerlessScope(Scope.PUBLIC)
 public class RestGetInferenceModelAction extends BaseRestHandler {
     @Override
     public String getName() {

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

@@ -10,6 +10,8 @@ package org.elasticsearch.xpack.inference.rest;
 import org.elasticsearch.client.internal.node.NodeClient;
 import org.elasticsearch.rest.BaseRestHandler;
 import org.elasticsearch.rest.RestRequest;
+import org.elasticsearch.rest.Scope;
+import org.elasticsearch.rest.ServerlessScope;
 import org.elasticsearch.rest.action.RestToXContentListener;
 import org.elasticsearch.xpack.core.inference.action.InferenceAction;
 
@@ -18,6 +20,7 @@ import java.util.List;
 
 import static org.elasticsearch.rest.RestRequest.Method.POST;
 
+@ServerlessScope(Scope.PUBLIC)
 public class RestInferenceAction extends BaseRestHandler {
     @Override
     public String getName() {

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

@@ -10,6 +10,8 @@ package org.elasticsearch.xpack.inference.rest;
 import org.elasticsearch.client.internal.node.NodeClient;
 import org.elasticsearch.rest.BaseRestHandler;
 import org.elasticsearch.rest.RestRequest;
+import org.elasticsearch.rest.Scope;
+import org.elasticsearch.rest.ServerlessScope;
 import org.elasticsearch.rest.action.RestToXContentListener;
 import org.elasticsearch.xpack.core.inference.action.PutInferenceModelAction;
 
@@ -18,6 +20,7 @@ import java.util.List;
 
 import static org.elasticsearch.rest.RestRequest.Method.PUT;
 
+@ServerlessScope(Scope.PUBLIC)
 public class RestPutInferenceModelAction extends BaseRestHandler {
     @Override
     public String getName() {