support bandwidth_limit set by server plugin (#3271)

* support bandwidth_limit set by server plugin

* limiter at proxy level

* bandwidth_limit_mode

* updates tests for bandwidth_limit_mode default

* bandwidth_limit_mode as string

* add checkForSrv for bandwidth_limit_mode

* bandwidth_limit flags for sub cmds

* gci write

pkg/config/types.go

@@ -24,6 +24,9 @@ import (
 const (
 	MB = 1024 * 1024
 	KB = 1024
+
+	BandwidthLimitModeClient = "client"
+	BandwidthLimitModeServer = "server"
 )
 
 type BandwidthQuantity struct {