Support custom attributes on summary list action links

[colinrotherham]

We've spotted a requirement in our service to add attributes to the "Check Answers" action links.

I've added support via this pull request. Thanks!

{{ govukSummaryList({
  rows: [
    {
      actions: {
        items: [
          {
            text: 'Edit',
            attributes: {
              'data-attribute-1': 'ABC',
              'data-attribute-2': '123'
            }
          }
        ]
      }
    }
  ]
}) }}

[36degrees]

Makes sense to me, aside from the YAML change nick's flagged – just one minor comment about the changelog.

[colinrotherham]

@36degrees @NickColley All sorted. Thanks for the quick review

[36degrees]

Tickity tick tick ✅

Thanks, @colinrotherham!