feat(search): support prepend_search_result option (#155)

Author: kevinlin09

samples/GenerationStreamCall.java

@@ -109,12 +109,14 @@ public static void streamCallWithSearchOptions()
                 .prompt("联网搜索明天杭州天气如何？")
                 .enableSearch(true)
                 .resultFormat("message")
+                .incrementalOutput(true)
                 .searchOptions(SearchOptions.builder()
                         .enableSource(true)
                         .enableCitation(true)
                         .citationFormat("[ref_<number>]")
                         .searchStrategy("pro_max")
                         .forcedSearch(true)
+                        .prependSearchResult(true)
                         .build())
                 .build();
         Flowable<GenerationResult> result = gen.streamCall(param);

src/main/java/com/alibaba/dashscope/aigc/generation/SearchOptions.java

@@ -33,4 +33,13 @@ public class SearchOptions {
   /** 搜索互联网信息的数量。standard：在请求时搜索5条互联网信息; pro：在请求时搜索10条互联网信息。 默认值为standard */
   @SerializedName("search_strategy")
   private String searchStrategy;
+
+  /**
+   * Whether the first data packet in streaming output contains only
+   * search source information. Only effective when enable_source is
+   * true and in streaming mode. Default is false.
+   */
+  @SerializedName("prepend_search_result")
+  @Builder.Default
+  private Boolean prependSearchResult = null;
 }