[ML] Enable DeepSeek Completion (#124665)

Enable streaming Completion as well as Chat Completion

Author: prwhelan

x-pack/plugin/inference/src/main/java/org/elasticsearch/xpack/inference/services/deepseek/DeepSeekService.java

@@ -57,6 +57,7 @@ public class DeepSeekService extends SenderService {
         TaskType.COMPLETION,
         TaskType.CHAT_COMPLETION
     );
+    private static final EnumSet<TaskType> SUPPORTED_TASK_TYPES_FOR_STREAMING = EnumSet.of(TaskType.COMPLETION, TaskType.CHAT_COMPLETION);
 
     public DeepSeekService(HttpRequestSender.Factory factory, ServiceComponents serviceComponents) {
         super(factory, serviceComponents);
@@ -169,7 +170,7 @@ public TransportVersion getMinimalSupportedVersion() {
 
     @Override
     public Set<TaskType> supportedStreamingTasks() {
-        return EnumSet.of(TaskType.CHAT_COMPLETION);
+        return SUPPORTED_TASK_TYPES_FOR_STREAMING;
     }
 
     @Override