support HTTP(S)_PROXY env vars when a proxy is needed between github-actions-cache-server and GitHub

[frantjc]

currently, I do not see any way of configuring github-actions-cache-server to forward unknown requests through a proxy to reach GitHub. This leads to 502 Bad Gateway errors on such requests when running in an environment that needs to go through a proxy to reach GitHub.

The simplest solution that I can see would be to upgrade the image to use NodeJS 24 to support the NODE_USE_ENV_PROXY env var, which would add support for HTTPS_PROXY, HTTP_PROXY, and NO_PROXY when NODE_USE_ENV_PROXY=1