Suggesting some configurations

Most common thing to do after utilising KnpMenu, is overriding the template, I believe we can overcome this step by providing some config in a yaml file for example
```
knp_menu:
menu_class: 'navbar-nav me-auto mb-2 mb-lg-0'
menu_item_class: 'nav-item'
menu_item_link_class: 'nav-link'
current_class: 'active'
current_class_on_link: true
```
I'd be willing to put some time in this effort with some direction, I lack the confidence in providing a solution like this :)

No files or tests are named. Start by reviewing how KnpMenu currently handles template overrides, then determine where YAML configuration would connect to the listed menu and item classes. Done means the proposed configuration is supported and its effect on rendered menus is verified.

Written by the indexing model from the issue text.