Http Conn Pool Fix Reentrancy

Fixed a re-entrancy bug in the connection pool where attaching a pending stream to a ready connection could recursively trigger connection allocation and ready callbacks if the stream was synchronously reset. This is resolved by removing the pending stream from the queue before calling its initialization/ready callback. This behavior can be temporarily reverted by setting the runtime flag envoy.reloadable_features.conn_pool_fix_reentrancy to false.