create component to create avatar icons from initial(s)

[StephanWald]

See figma, we have many places where a picture can be replaced by an iconographic badge containing one or multiple letters, like
[M] for Microsoft or [BG] for Bill Gates.

Colors should be compliant with the theme file selected - do some research how to compute colors based on the letter and the theme.

Implement a component that can be used to add such a "badge" with one statement. (Maybe create a webcomponent like the ones in https://github.com/BasisHub/basis-next, get with the maintainer to discuss.)