feat: Add support for custom node http agent

[belemaire]

We have a complex enterprise CI infrastructure in which we have to go through a proxy to tunnel requests to external servers.

One way to make http(s) requests go through a proxy in Node.js is to setup a custom http agent and pass it in http.request options.

This PR updates some functions to propagate the options that were set by the client. Ultimately, the request call will set the agent in the http.request options if it is set in client provided options.

Please note that this agent option is only exposed through programmatic usage of the package (that's our usage of it). It is not surfaced as a new CLI option (would be complex to). That being said, as a follow up of this PR, one could update the CLI to expose a new http-proxy option, for user to pass a proxy url, and internally could make use of tunnel -or other lib-, to create an agent from this url and pass it to the upload options so that it gets set in the http request.

[xljones]

Hey @belemaire, thanks for the PR. We'll need to do some work on this to review the changes, and see what other updates we'll need to make if we integrate this. We won't be able to schedule for a while due to some of our other priorities.

I've raised this on our backlog to take a look at when time permits. For now you could fork the repository to start using your fix. Thanks again --Xander

[abigailbramble]

Released in v1.3.0