Allow custom pagination buttons

[ciampo]

Allow a <slot> element
Think about specs for what type of element is allowed as "pagination"

It may be difficult as the slider adds/removes pagination buttons.

Maybe split pagination and navigation into a separate component and expect as a replacement something with the same APIs

[ciampo]

Idea: split the pagination in a separate WC, and also provide a different type of pagination (e.g. a progress bar)