add flush elasticsearch bulk action option

[niroshea]

目前 flusher_elasticsearch 扩展插件写入数据只有index模式，为了解决该问题，我在插件配置中新增一个Action选项，方便用户填入比如 create、 update等写入模式。
elasticsearch 的一些常用场景比如 datastream 只支持create模式写入数据。
与已有配置保持了兼容，如果用户没有配置Action选项，默认还是index模式。

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✅ niroshea
❌ shebinbin

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