fix(测试跟踪): 富文本框自定义字段输入提示没有国际化

--story=1015721 --user=陈建星 【三星】测试用例模板：自定义字段类型为富文本类型，功能测试用例明细中，支持放在左侧，和默认的字段（前置条件和步骤描述）展示形式一样 https://www.tapd.cn/55049933/s/1566955

framework/sdk-parent/frontend/src/components/new-ui/MsCustomFiledComponent.vue

@@ -125,6 +125,7 @@
                        :prop="prop"
                        @change="handleChange"
                        :default-open="defaultOpen"
+                       :placeholder="$t('commons.input_content')"
                        :data="data" :disabled="disabled"/>
 
     <el-input v-else-if="data.type === 'password'"

framework/sdk-parent/frontend/src/i18n/lang/en-US.js

@@ -241,7 +241,7 @@ const message = {
     please_save: "Please save first",
     formatErr: "Format Error",
     id: "ID",
-    cannot_be_null: "not null ",
+    cannot_be_null: " not null ",
     required: "{0} is required",
     millisecond: "ms",
     please_upload: "Please upload file",