Add TUNNEL_PROXY support to AsyncConnectExec for proxy chain tunneling

[arturobernalg]

Implement async handling of multi-hop proxy routes with CONNECT requests Update test to verify successful proxy chain establishment

[ok2c]

@arturobernalg Have you been able to test it in real-life settings with multiple proxy servers forming a proxy chain?

Then, we would also need to make similar changes to the classic ConnectExec.

[arturobernalg]

@arturobernalg Have you been able to test it in real-life settings with multiple proxy servers forming a proxy chain?

Then, we would also need to make similar changes to the classic ConnectExec.

The classic already have a implementations --> https://github.com/apache/httpcomponents-client/blob/master/httpclient5/src/main/java/org/apache/hc/client5/http/impl/classic/ConnectExec.java#L165

[ok2c]

@arturobernalg Have you been able to test it in real-life settings with multiple proxy servers forming a proxy chain?
Then, we would also need to make similar changes to the classic ConnectExec.

The classic already have a implementations --> https://github.com/apache/httpcomponents-client/blob/master/httpclient5/src/main/java/org/apache/hc/client5/http/impl/classic/ConnectExec.java#L165

@arturobernalg That code is likely wrong or broken or both. There is not a single integration test case that exercises it. Instead of adding similarly broken code in the async pipeline we should rather remove it from the classic one.