Support changing download source in postinstall

[typed-sigterm]

Is your feature request related to a problem? Please describe.
You know what GFW had being doing😶

cli/scripts/postinstall.js

Line 44 in d8fe26d

const url = `https://github.com/${repo}/releases/download/v${version}/${pkgName}_${platform}_${arch}.tar.gz`;

cli/scripts/postinstall.js

Line 52 in d8fe26d

const checksumFileUrl = `https://github.com/${repo}/releases/download/v${version}/${pkgName}_${version}_checksums.txt`;

Describe the solution you'd like
Read template string from an environment variable to replace the hard-coded url.

[sweatybridge]

Do you have the error logs by any chance? I believe we are already handling https_proxy variables using https-proxy-agent package.

[typed-sigterm]

Do you have the error logs by any chance? I believe we are already handling https_proxy variables using https-proxy-agent package.

That's fixed after rebooting :)