router: add RefreshBackend method for Router interface

pkg/manager/router/router.go

@@ -38,6 +38,7 @@ type Router interface {
 	ConnEventReceiver
 
 	GetBackendSelector() BackendSelector
+	RefreshBackend()
 	RedirectConnections() error
 	ConnCount() int
 	// ServerVersion returns the TiDB version.

pkg/manager/router/router_score.go

@@ -186,6 +186,11 @@ func (router *ScoreBasedRouter) adjustBackendList(be *glist.Element[*backendWrap
 	}
 }
 
+// RefreshBackend implements Router.GetBackendSelector interface.
+func (router *ScoreBasedRouter) RefreshBackend() {
+	router.observer.Refresh()
+}
+
 // RedirectConnections implements Router.RedirectConnections interface.
 // It redirects all connections compulsively. It's only used for testing.
 func (router *ScoreBasedRouter) RedirectConnections() error {

pkg/manager/router/router_static.go

@@ -50,6 +50,8 @@ func (r *StaticRouter) GetBackendSelector() BackendSelector {
 	}
 }
 
+func (r *StaticRouter) RefreshBackend() {}
+
 func (r *StaticRouter) RedirectConnections() error {
 	return nil
 }