fix(i18n): refine default source label in English and Chinese locales

dashboard/src/i18n/locales/en-US/features/extension.json

@@ -90,7 +90,7 @@
     "addSource": "Add Source",
     "sourceName": "Source Name",
     "sourceUrl": "Source URL",
-    "defaultSource": "Official Source",
+    "defaultSource": "Default Source",
     "removeSource": "Remove Source",
     "confirmRemoveSource": "Are you sure you want to remove this source?",
     "sourceAdded": "Source added successfully",

dashboard/src/i18n/locales/zh-CN/features/extension.json

@@ -90,7 +90,7 @@
     "addSource": "添加插件源",
     "sourceName": "源名称",
     "sourceUrl": "源地址",
-    "defaultSource": "官方插件源",
+    "defaultSource": "默认插件源",
     "removeSource": "删除插件源",
     "confirmRemoveSource": "确定要删除此插件源吗？",
     "sourceAdded": "插件源添加成功",