[Accessibility] Unified keyboard focus highlight for UI components

[joelit]

Description of the enhancement

• There are various visuals for showing keyboard focus (ad-hoc solutions, bootstrap defined and browser native)

• They need to be unified in a way that makes sense in the Skosmos colour palette

• Decide how the keyboard focus should look like and check the design across different contexts

• Implement the keyboard focus in CSS

• Apply the focus across the different elements

What new functionalities would the enhancement make possible?

• having an easy way for handling focus in CSS makes it easy to keep the same logic accross old and new Skosmos UI components and plugins