feature: Add Exercism public profile in Social section (fixes #761)

[RianNegreiros]

What type of PR is this? (check all applicable)

• Refactor
• Feature
• Bug Fix
• Enhancement
• Documentation Update

Description

• Added support for displaying Exercism public profile in the social section.
• Added an Exercism logo SVG file from the Exercism website-icons repository.
• Added the exercism field to DEFAULT_SOCIAL.
• Updated the Social component to include Exercism input field.
• Updated the Markdown and Markdown Preview to display the Exercism icon, redirecting to user profile.

Related Tickets & Documents

Closes #761

QA Instructions, Screenshots, Recordings

1. Find Exercism input field:
   
2. Insert your Exercism username:
   
3. Check the generated markdown:
   
4. Check the markdown preview (used link from my branch for the test):
   

Demo

Added to documentation?

• readme