consider about adding a connection resource control module for proxy

[cherrylzhao]

now our proxy backend connection model was based on channel after connection was established.
if client side use asynchronous connection model, our proxy will make the request per on channel synchronized for resource controller, and backend connection self became very heavy.

so we consider about simplify backend connection. make backend connection multi-instances available within one established channel. maybe we can add a resource controller module for proxy.
it will allocate the physical connection resource according to sql explain plan, transaction, customized configuration.

[cherrylzhao]

just close it since we have not plan to refactor it.