feat: add support for .kbwf file uploads in el-upload component

--bug=1065076 --user=刘瑞斌 【知识库】工作流知识库中导入工作流，可选文件没有进行类型过滤 https://www.tapd.cn/62980211/s/1818699

Author: liuruibin

ui/src/views/knowledge-workflow/index.vue

@@ -63,6 +63,7 @@
               <el-upload
                 class="import-button"
                 ref="elUploadRef"
+                accept=".kbwf"
                 :file-list="[]"
                 action="#"
                 multiple