Adding url configuration field

Author: jonathan-buttner

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

@@ -60,6 +60,7 @@
 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 static InferenceServiceConfiguration get() {
             () -> {
                 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(