Cache plugin design issue

[AndyManastorm]

https://github.com/serverless-cd/website/blob/main/docs/user-guide/plugins/cache.md

Hi, I have several suggestions about the cache plugin designation.

• GC strategy like TTL should be provided as a convention or configuration, so that storage costs are not incurred for outdated data.
• Cache update strategy like update-after or never or always should be provided as a configuration. But it seems like that cache plugin's lifecycle beyonds its step.
• According to the README, cache data will be stored in an OSS bucket, but I can't find any descriptions about the mapping stragety.
• The output object for cache plugin should be clearly defined in the README.