Mount a COS based volume for caching

What does this MR do and why?

“顺序分配Feature Flag Change Issue 的 Assignee” 功能需要 Web 应用有一个持久化的目录 ./cache，由于是多副本部署，因此需要共享卷作为存储。

目前腾讯云支持 COS 和 NFS，由于 COS 的 terraform module 已经具备，因此先尝试采用 COSFS 的卷。

相关 issue： #65 (comment 1699104)

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