separate lock from common grid to avoid epoll contention (#20180)

epoll contention on TCP causes latency build-up when
we have high volume ingress. This PR is an attempt to
relieve this pressure.

upstream issue https://github.com/golang/go/issues/65064
It seems to be a deeper problem; haven't yet tried the fix
provide in this issue, but however this change without
changing the compiler helps. 

Of course, this is a workaround for now, hoping for a
more comprehensive fix from Go runtime.

cmd/lock-rest-client_test.go

@@ -39,7 +39,7 @@ func TestLockRESTlient(t *testing.T) {
 
 	ctx, cancel := context.WithCancel(context.Background())
 	defer cancel()
-	err = initGlobalGrid(ctx, []PoolEndpoints{{Endpoints: Endpoints{endpoint, endpointLocal}}})
+	err = initGlobalLockGrid(ctx, []PoolEndpoints{{Endpoints: Endpoints{endpoint, endpointLocal}}})
 	if err != nil {
 		t.Fatal(err)
 	}