Allow passing custom class to the post pagination functions

[jfarthing84]

The functions the_posts_pagination() and get_the_posts_pagination() should accept a class to be used instead of only defaulting to .pagination.

If anyone wishes to achieve this meanwhile, it must be done with the navigation_markup_template filter, unfortunately:

<?php
function navigvation_markup_template_filter( $template, $class ) {
        if ( 'pagination' == $class ) {
                $template = str_replace( '%1$s', 'posts-pagination', $template );
        }
        return $template;
}
add_filter( 'navigation_markup_template', 'navigvation_markup_template_filter', 10, 2 );