Add new --proxy-cache option

[shuizhongyueming]

Add a new option --proxy-cache to cache response from the proxy server and will auto decompress the response if it is compressed based on the content-encoding header

Contributor checklist

• Provide tests for the changes (unless documentation-only)
• Documented any new features, CLI switches, etc. (if applicable)
  • Server --help output
  • README.md
  • doc/http-server.1 (use the same format as other entries)
• The pull request is being made against the master branch

Maintainer checklist

• Assign a version triage tag
• Approve tests if applicable

[github-actions]

This pull request has been inactive for 360 days

[KernelDeimos]

After manually testing and reviewing this code I've come to understand that this is half a proxy implementation - it writes every proxied response to a file, overwriting the file if a proxied response already exists there. There is only one file so, effectively, this is just a local file that contains the last response and is not used by http-server when generating responses. Merging this as-is would introduce a performance overhead.

What is this flag meant to be used for?