Replace router svcAddrUpdateLocks with new throttler package for code readability&reusability (#1047)

Rename svcAddrUpdateLock to Throttler and move it to the top-level directory as a package for code import.

router/router.go

@@ -54,6 +54,7 @@ import (
 	"github.com/fission/fission"
 	"github.com/fission/fission/crd"
 	executorClient "github.com/fission/fission/executor/client"
+	"github.com/fission/fission/throttler"
 )
 
 // request url ---[mux]---> Function(name,uid) ----[fmap]----> k8s service url
@@ -150,7 +151,7 @@ func Start(port int, executorUrl string) {
 		keepAlive:         keepAlive,
 		maxRetries:        maxRetries,
 		svcAddrRetryCount: svcAddrRetryCount,
-	}, isDebugEnv, MakeUpdateLocks(svcAddrUpdateTimeout))
+	}, isDebugEnv, throttler.MakeThrottler(svcAddrUpdateTimeout))
 
 	resolver := makeFunctionReferenceResolver(fnStore)