MySQL - Add username customization (#10834)

plugins/database/mysql/mysql-database-plugin/main.go

@@ -19,7 +19,7 @@ func main() {
 // Run instantiates a MySQL object, and runs the RPC server for the plugin
 func Run() error {
 	var f func() (interface{}, error)
-	f = mysql.New(mysql.MetadataLen, mysql.MetadataLen, mysql.UsernameLen)
+	f = mysql.New(mysql.DefaultUserNameTemplate)
 	dbType, err := f()
 	if err != nil {
 		return err