function getProxySettings(env) {
  return Object.entries(env)
    .filter((entry) => PROXY_ENV_VARIABLES.includes(entry[0].toUpperCase()))
    .filter((entry) => entry[1] !== '')
    .map((entry) => `${entry[0]}=${entry[1]}`);
}
Expects an environment variables object (typically process.env)
and returns an array of strings representing HTTP proxy settings,
such as ['HTTPS_PROXY=https://proxy.example.com:8080', ...]

Supports both upper and lower case names and skips env vars set as empty
strings (other falsy values are not taken care of as env vars can only
be strings).

Note: The settings are later only printed to the user. Applying the settings
is handled directly by the 'request' library, see
https://github.com/request/request#user-content-proxies