Ensure Proxy Support about cli

[dshafik]

@francescoc-vf due to the architecture of the CLI, environment variables are the primary way of communicating with the package commands - this means adding a global proxy flag would likely just set the HTTP_PROXY environment variable before forking off the child process.

If this is acceptable, that is fine.

[francescoc-vf]

Thanks for your prompt answer but proxy support via environment variable does not satisfy my request in #41.

Main target for this utility is supporting DevOps environments; meaning jumpservers, buildservers, monitoring servers.

While an environment variable is an acceptable solution on a personal workstation it's not recommended and usually forbidden in these scenarios.

There are also many other concerns about security and network complexity which really mandates a command line switch.

I'd suggest to consider that all other cli tools in this class (curl, wget, aria, httpie) does support it, usually on top of the environment variable.
Otherwise the value of this tool will be limited to a few very specific use cases.

[francescoc-vf]

Sorry my bad, didn't explain myself properly :)
There are some limitations where you are not in control of the environment.
Setting up a proxy through a variable is not acceptable while it's "tolerated" via command line switch.

[dshafik]

@francescoc-vf I understand, I'll look to add this flag, which will just set the environment variable for sub-commands.

[dshafik]

@khunter has confirmed that Node packages do support HTTP_PROXY.

[rajiv]

ruby plugins which use the akamai/AkamaiOPEN-edgegrid-ruby gem (and consequently Net::HTTP in ruby) support http_proxy, and print this warning with HTTP_PROXY:

The environment variable HTTP_PROXY is discouraged.  Use http_proxy.