feat: 完善清洗模板字段处理

[JunLong-Lin]

No description provided.

[yiqiwang-17]

整体方向认可：etl_storage/base.py:1064 确实是 field["is_dimension"] 硬取，历史模板缺该键会 500；模板 serializer 从自由 DictField 收紧也能挡住脏数据。

但有 3 条 P1 建议修完再合，已按位置发在对应行：

1. 兜底只补了 is_dimension，同一批历史模板缺 is_delete 等键时仍会 500（transfer.py）。
2. etl_params 换成 Serializer 后会把 DRF 默认值写进模板，其中 record_parse_failure 会被强制置 True，与采集项侧联动语义相反（serializers.py:1177）。
3. etl_fields 校验收紧属不兼容变更，且本次收紧零测试覆盖（serializers.py:1178）。

另外 PR 描述为空，建议把上述行为变化（尤其是模板 etl_params 持久化内容的变化）补进描述，方便后续回溯。

[codecov-commenter]

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