[ML] Exposing OpenAI URL field in services API (#126638) (#126684)

* Adding url configuration field

* Fixing test

x-pack/plugin/inference/src/main/java/org/elasticsearch/xpack/inference/services/openai/OpenAiService.java

@@ -60,6 +60,7 @@ import java.util.Set;
 import static org.elasticsearch.xpack.inference.external.action.ActionUtils.constructFailedToSendRequestMessage;
 import static org.elasticsearch.xpack.inference.services.ServiceFields.DIMENSIONS;
 import static org.elasticsearch.xpack.inference.services.ServiceFields.MODEL_ID;
+import static org.elasticsearch.xpack.inference.services.ServiceFields.URL;
 import static org.elasticsearch.xpack.inference.services.ServiceUtils.createInvalidModelException;
 import static org.elasticsearch.xpack.inference.services.ServiceUtils.parsePersistedConfigErrorMsg;
 import static org.elasticsearch.xpack.inference.services.ServiceUtils.removeFromMap;
@@ -418,6 +419,19 @@ public class OpenAiService extends SenderService {
             () -> {
                 var configurationMap = new HashMap<String, SettingsConfiguration>();
 
+                configurationMap.put(
+                    URL,
+                    new SettingsConfiguration.Builder(SUPPORTED_TASK_TYPES_FOR_SERVICES_API).setDescription(
+                        "The absolute URL of the external service to send requests to."
+                    )
+                        .setLabel("URL")
+                        .setRequired(false)
+                        .setSensitive(false)
+                        .setUpdatable(false)
+                        .setType(SettingsConfigurationFieldType.STRING)
+                        .build()
+                );
+
                 configurationMap.put(
                     MODEL_ID,
                     new SettingsConfiguration.Builder(SUPPORTED_TASK_TYPES_FOR_SERVICES_API).setDescription(

x-pack/plugin/inference/src/test/java/org/elasticsearch/xpack/inference/services/openai/OpenAiServiceTests.java

@@ -1589,6 +1589,15 @@ public class OpenAiServiceTests extends ESTestCase {
                                     "type": "str",
                                     "supported_task_types": ["text_embedding", "completion", "chat_completion"]
                                 },
+                                "url": {
+                                    "description": "The absolute URL of the external service to send requests to.",
+                                    "label": "URL",
+                                    "required": false,
+                                    "sensitive": false,
+                                    "updatable": false,
+                                    "type": "str",
+                                    "supported_task_types": ["text_embedding", "completion", "chat_completion"]
+                                },
                                 "dimensions": {
                                     "description": "The number of dimensions the resulting embeddings should have. For more information refer to https://platform.openai.com/docs/api-reference/embeddings/create#embeddings-create-dimensions.",
                                     "label": "Dimensions",