HTTP Proxy Support for ZET with basic authentication

[shekahamed]

1. Add HTTP Proxy Support in Ziti Edge Tunnelers with basic authentication. This functionality will cater to enterprise network/security environments to deploy ZET behind the proxy where it is relatively easier for policy changes on the proxy to allow the DNS / IP of the CloudZiti controller and public fabric routers, rather than on a firewall.
2. Introduce new configuration options for ZET to enable basic authentication with HTTP proxies. This could involve:

• Username and password fields for basic authentication with HTTP proxy.
• Configuration option for the proxy server address and port.