monitoring: some bug fix

Signed-off-by: huanggze <loganhuang@yunify.com>

pkg/models/monitoring/expressions/registry.go

@@ -4,6 +4,6 @@ type labelReplaceFn func(expr, ns string) (string, error)
 
 var ReplaceNamespaceFns = make(map[string]labelReplaceFn)
 
-func Register(name string, fn labelReplaceFn) {
+func register(name string, fn labelReplaceFn) {
 	ReplaceNamespaceFns[name] = fn
 }