Add markup for avatars

[michaeltlombardi]

As a site maintainer, I want to be able to add avatar displays for my team members without having to code everything myself.

Suggested Implementation:

Image link render hook for the sl-avatar element that:

• Uses the alt text for the label
• Uses the destination for the image source
• Supports presets in the destination with the prefix preset
• Supports shapes, icons, and classes