BE: fix(rbac): revert remove defaultRole setter

Author: seonho-jeong

api/src/main/java/io/kafbat/ui/config/auth/RoleBasedAccessControlProperties.java

@@ -27,6 +27,10 @@ public List<Role> getRoles() {
     return roles;
   }
 
+  public void setDefaultRole(DefaultRole defaultRole) {
+    this.defaultRole = defaultRole;
+  }
+
   @Nullable
   public DefaultRole getDefaultRole() {
     return defaultRole;