Support custom yamux.Config

[mickmister]

When using the dlv debugger, the plugin's RPC call will be terminated while the debugger is paused. I have gotten around this by making this change in

go-plugin/rpc_client.go

Line 63 in a02e5c7

mux, err := yamux.Client(conn, nil)

- 	mux, err := yamux.Client(conn, nil)
+	sessionConfig := yamux.DefaultConfig()
+	sessionConfig.EnableKeepAlive = true
+	sessionConfig.ConnectionWriteTimeout = time.Minute * 5
+	mux, err := yamux.Client(conn, sessionConfig)

Is it possible to allow for a config like this, or an alternative way to avoid having the RPC connection be interrupted?