Bump app version to 5.28 (#15005)

model/version.go

@@ -13,6 +13,8 @@ import (
 // It should be maintained in chronological order with most current
 // release at the front of the list.
 var versions = []string{
+	"5.28.0",
+	"5.27.0",
 	"5.26.0",
 	"5.25.0",
 	"5.24.0",