Support for accessing Azure repositories through a proxy

[astefan]

Consider adding support for accessing an Azure snapshot repository through a proxy. At the moment, the only closely related option is to use https.proxyPort/Host java options, which are ignored for this type of Azure access.

[dadoonet]

We need first to implement #23448 so we will be able to do something like:

OperationContext.setDefaultProxy(new Proxy(Proxy.Type.HTTP, new InetSocketAddress("10.1.1.1", 8888)));

Which has been added since v4.2.0.