feat: added configuration center function (#3035)

Co-authored-by: aiden.ma <Aiden.ma@yijinin.com>

core/configcenter/subscriber/subscriber.go

@@ -0,0 +1,9 @@
+package subscriber
+
+// Subscriber is the interface for configcenter subscribers.
+type Subscriber interface {
+	// AddListener adds a listener to the subscriber.
+	AddListener(listener func()) error
+	// Value returns the value of the subscriber.
+	Value() (string, error)
+}