all: add pull API config based on special DNS query

For query domain that matches "uid.verify.controld.com" in cd mode, and
the uid has the same value with "--cd" flag, ctrld will fetch uid config
from ControlD API, using this config if valid.

This is useful for force syncing API without waiting until the API
reload ticker fire.

cmd/cli/cli.go

@@ -1141,6 +1141,7 @@ func run(appCallback *AppCallback, stopCh chan struct{}) {
 		reloadDoneCh:     make(chan struct{}),
 		dnsWatcherStopCh: make(chan struct{}),
 		apiReloadCh:      make(chan *ctrld.Config),
+		apiForceReloadCh: make(chan struct{}),
 		cfg:              &cfg,
 		appCallback:      appCallback,
 	}