docs: Add avatar with tooltip examples

This MR adds examples of how to display a tooltip in an avatar component.

Initially, I planned to implement "tooltip support" like we do in the avatar component in gitlab (see avatar_image and avatar link) but I noticed that just adds unnecessary complexity to the Avatar component.

bootstrap-vue encourages to use the tooltip component as a Vue directive. IMO it makes sense because it is a more compositional and transparent approach than embedding a tooltip component within the avatar.

So instead of implementing something new, I decided to build examples to show how to use avatars and tooltips together.

Closes #383 (closed)