fix(news-ticker): Fix accessibility issues - FRONT-3634

[papegaill]

• The newsticker is not fully keyboard operable: the buttons for the next and previous items do not receive keyboard focus. Make sure the buttons can be reached with the TAB key and activated with the ENTER key (remove the tabindex attribute).
  • already done since 3.3.0
• The buttons for the next and previous items are not labelled. Provide text inside the button or use aria-label.
  • already done since 3.3.0
• The button to start and pause the ticker is not labelled. Provide text inside the button or use aria-label.
  • already done since 3.3.0
• The items inside the ticker are focusable but hidden from screen readers with aria-hidden. Remove the aria-hidden
  • fixed in this PR
• Best practice recommendations: Pause the ticker automatically when the keyboard focus is on a news item in the ticker. Users who need a bit more time to complete actions will very much appreciate this.
  • added in this PR

NB: I'm also fixing following styles issues (since 3.3.0)

• margin issue with button icons
• alignment of the counter on mobile version

[github-actions]

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