fix: a11y for columns and edit content

[Wagner3UB]

• 2 new regions created for landmarks ("Column selection" and "Edit column content")
• The tabs now contain buttons instead of regular links
• All buttons with a proper label inside the tabs
• The "+" now is a button with a proper label

Note:
The aria-labels for Menu.Item and Button.Group are quite different because of a condition, with or without title. It's basically 2 default messages together if the title isn't set. I couldn't use props as I would like, using only one id because the condition doesn't allow me to translate the second part of the sentence.

aria-label={intl.formatMessage(messages.column) + ' ' + (idx + 1) + ' ' + (footerColumn.title ?? intl.formatMessage(messages.no_title))}