Banner > Default aria-label for BannerComponent close button

The following discussion from !89425 (merged) should be addressed:

• @dpisek started a discussion: (+1 comment)

  question: This might be slightly outside the scope of this MR, but I saw that you are the author of Pajamas::BannerComponent, so I'll take the chance to ask 🙂

  Should 'aria-label' => _('Dismiss') be the default for the banner's dismiss-button? And maybe make it so that close_options can override the label-text?

  I feel like the aria-label should be present at all times 🤔