HTTP.rb should support setting proxy via standard unix ENV variables: `http_proxy` and `https_proxy`

This is a follow up from #10586 (closed).

We are using HTTP.rb library for the Object Storage replication and for the Container Registry replication. Its also being used as dependency by kubeclient. This gem currently doesn't support the UNIX standar ways of defining proxy by setting environmental variables: http_proxy and https_proxy.

I've contacted the upstream project in the already open issue: https://github.com/httprb/http/issues/356 and they are willing to accept a pull request to introduce the support for this kind of feature.

Risk analysis

With regards to Container Registry, there is a minimal chance the lack of this support will affect it in any way, as usually a container registry will not be behind the network that is accessible only by the proxy.

In the case of Object Storage, the risk is slightly bigger, as you may have a situation where you are hosting the main application locally, but using an external object storage solution (ex, in a hybrid cloud installation).

Considering the kubeclient, the risk is similar to object storage. It may only be a problem if they have an hybrid setup where something is colocated and something is on an external cloud provider (or running in a different datacenter, routed through the open internet).