Create an example for `MultiAddressHttpClientBuilder.SingleAddressInitializer`

[idelpivnitskiy]

Demonstrate how MultiAddressHttpClientBuilder.SingleAddressInitializer can be used to configure underlying clients based on host and port.

An example can be based on one of the http/helloworld examples. Not necessary to repeat all 4 API variants. The goal is only to demonstrate builder features. For example, users can use SingleAddressInitializer to configure SSL certs for https targets or apply a logging filter only for specific host and port. Example should run 2 different servers and one MultiAddressUrlClient to demonstrate it can communicate with both servers.