Provide additional field for set some css classes directly to <a> element in navigation-link block

[cawa-93]

What problem does this address?

The navigation block is extremely limited. You cannot insert a Button block into the navigation. You can't even copy and paste classes into a link, because classes are pasted into the parent <li>, not the <a>.

Currently, there is no easy way to somehow increase the height of the link. You can't set a minimum height, can't add padding, nothing. The only option available to you is to add classes to <li> and then edit the css to apply the styles not to the element with the class but to the child element <a>

What is your proposed solution?

Provide additional field for set some css classes directly to <a> element.

[mrfoxtalbot]

Related to #49415