Metrics can be lost if backhual is not available for more than 10 minutes [future issue]

Given the current metrics service implementation if we cannot publish metrics over HTTP for more than 10 minutes we will start to lose metrics payloads, this can leave chunks of delta values missing which will cause future metrics to be incorrect. We need to think of a scalable way to preserve metrics if a publish fails, perhaps by cycling metrics back into the timed cache or processing cache if they cannot be immediately sent, an infinitely sized queue could also be used but this will not scale well

先檢視目前的 metrics service 實作，尤其是 HTTP 發佈流程周圍使用的 timed cache 與 processing cache。確認失敗的發佈如何處理，並設計可擴充的保存方案；當 metrics payloads 在超過 10 分鐘的中斷期間不會遺失，且未來的 delta values 仍然正確時，即視為完成。

由索引模型根據 Issue 內容生成。