[proxy_agent_shared] WS & HostGAP clients setup

[bingyuyin]

Changes summary:

1. move common from proxy_agent to proxy_agent_shared so that the http client hyper_client could be reused
2. set up wire-server and hostga plugin client basic api calls
3. certificates helpers for create self sign certificate and decrypt using certificate [windows only]

to-do:

1. merge proxy_agent wire_server client with shared