Has a dependency on AvatarBase #390

Description

This PR adds a new AvatarFavicon component to the design system.

Key features:

• Displays dapp favicon/logo images with consistent sizing and styling
• Provides text fallback when image is not available (uses first letter of name or custom fallback text)
• Supports multiple sizes (xs, sm, md, lg, xl) with appropriate text scaling
• Handles alt text and accessibility concerns
• Allows customization of both image and fallback text properties

Related issues

Fixes: #368

Manual testing steps

1. Run storybook (yarn storybook)
2. Navigate to React Components/AvatarFavicon
3. Test different component configurations:
   • With and without image source
   • Different sizes
   • Custom fallback text
   • Custom styling via className and props

Screenshots/Recordings

Before

N/A - New component

After

Pre-merge author checklist

• I've followed MetaMask Contributor Docs
• I've completed the PR template to the best of my ability
• I've included tests for the new AvatarFavicon component
• I've documented the code using JSDoc format
• I've applied the right labels on the PR

Pre-merge reviewer checklist

• I've manually tested the PR (e.g. pull and build branch, run storybook, test AvatarFavicon component)
• I confirm that this PR addresses all acceptance criteria described in the ticket it closes and includes the necessary testing evidence such as recordings and or screenshots