--create-release option for version behind proxy server

[p-m-p]

I appreciate the project is in a bit of a transition period but with a little direction I'd be happy to provide a PR to address the issue I am currently facing.

Expected Behavior

lerna version --conventional-commits --create-release should work or be configurable to work behind a proxy server.

Current Behavior

Specifically for the Github client there doesn't appear to be support to pick up or provide http proxy configuration for the octokit library options.request.agent

Possible Solution

Automatically pick up environment variables or provide configuration option to configure the proxy. Perhaps along the lines of how this is done in semantic-release