Add variable for nav-link padding in navbar nav

[Kopyov]

Currently .nav-link in navbar nav has 0.5rem horizontal padding defined in _navbar.scss. If i want to override these values, i get all breakpoint classes with new values on top of the current ones. Would be better to change it to some variable for better overriding capability so that i can override them without adding new CSS.

[andresgalante]

Yes, you are right, A PR has been submitted to fix it here #23109

[Johann-S]

duplicate of #23034